Does This Look Broken?

[Paradise3]

Right so a bit of background history. When my fiance shut his tank down I inherited his fish. 
A total of
2x Adult female mollies and about 50 babies.
4x Female Jordanella floridae(Flagfish)
1x Farlowella catfish
100+ Cherry Shrimp
&
1x Male platy.
 
I re-homed the mollies as they were bullying everyone else in the tank.
The four flagfish became three.... The three I have now bullied the fourth to death. Now they are ripping everyone else to shreds including the third flagfish. Yep, they bullied the fourth and now two are bullying the third. I know they can be a bit aggressive but they were fine for weeks and then this. All hell has broke loose in my tank because of these flagfish. I desperately wanted to keep them but I eventually decided to re-home. And then there's this. I spotted this on Friday and so now I'm stuck with them until I either figure it out or she heals.
 
In the time since spotting it I have meth blue bathed her, thinking it was fungal and it would show up. Nope... There is no visible external injury, just the very obvious lump which seems to be underneath.
 
It literally appeared overnight. Thursday night they were all fine, Friday morning she was like this. She's still swimming fine, eating, acting normal, etc... In the time that this has happened all three flagfish have gone mental against my other fish! My poor betta is shredded, he's more plakat than halfmoon now. My female guppy* is practically crowntailed right now...
I am at a loss, I have IAL in the tank but nothing is helping anyone while the fighting is still going on and the fighting won't stop until the flagfish are gone but the flagfish can't go until she's healed! Help?!
 
Tank stats
Size: 2ft - 15 gallons.
Temperature: 26c - 78.8f.
Parameters: Ammonia - 0ppm, Nitrite - 0ppm, Nitrate - Between 5-10ppm.
Fish/Invert Stock: Admittedly overstocked currently. Still thinning them out.
1x Female guppy - Planned re-home when healed.
4x Male Endler Hybrids - Strangely not interested in the female and not had any fry from them.
1x Male Betta.
1x Farlowella Catfish.
2x Otocinclus catfish.
3x Platies - 1 male, 2 female - No fry.
3x Female Flagfish.
100+ Cherry Shrimp.
About 5 Assassin Snails - Probably more, I never see more than five but I have seen empty egg pockets...
Plant/Decor Stock: Rocks, redmoor wood and the following plants.
Cryptocoryne beckettii
Nymphoides ap. "Taiwan".
Hygrophila polysperma
Hygrophila corymbosa
Pictures: Below are pictures of her injury. I had to take her out, put her in a small clear pot on top of the wire lid(don't even ask about that lol) so that the light was behind her to look at her bone structure and see if there was visible breakage. There seems to be something there but I'm not sure it's a break. As you can see she has a few nips in her tail too.

 
Any help or suggestions are appreciated.
 
P.S. Please no-one say anything about a female guppy living with a fighter, she helped him. He went through a stage of tail biting, someone suggested it and I was really against it(I disagree with guppies with betta's) but they insisted I at least tried it. It was a risk but he was biting himself badly so I tried it, with a back up plan of course. It worked, he stopped biting himself but he didn't care about her either. I'm worried removing her will start his biting off but leaving her there is a huge risk and I'd rather not leave it much longer... If anyone has any other suggestions in case he starts biting again when she's gone? Having a guppy in the tank is a disaster waiting to happen...

 

[star4]

It looks like she has some internal damage and fluid build up. This should heal but she maybe left with a kink before her tail, this shouldnt affect her, I have a fish here with the same, had her for years. Flag fish are very nippy, and for a small fish they need a large tank with masses of plant cover and algae to keep them occupied. They really do not do well in an overcrowded tank. If you can add a load of floating plants this will help with the aggression between them, but it wont stop them going for the other fish.

 

[Paradise3]

It looks like she has some internal damage and fluid build up. This should heal but she maybe left with a kink before her tail, this shouldnt affect her, I have a fish here with the same, had her for years. Flag fish are very nippy, and for a small fish they need a large tank with masses of plant cover and algae to keep them occupied. They really do not do well in an overcrowded tank. If you can add a load of floating plants this will help with the aggression between them, but it wont stop them going for the other fish.

 
Thanks, they aren't staying here that's for sure. I don't have the facilities to house them correctly for life. My fiancé shutting down his tank was a last minute decision, he was meant to wait until he had sold the fish first. The ones I wanted were the farlowella, the male platy and the cherry shrimp. No flagfish, no mollies...
 
Unfortunately I have no money so floating plants it a no go at the minute, as for algae... If they'd eat BBA they'd have had loads for them recently but instead they chose to ignore that and attack the fish instead. Most likely due to the lack of plant life after the BBA as well as tannins blocking light out caused a lot of plant life to perish

 

[attibones]

Have you got a spare tank lying around? I'm thinking you need to remove the other flags, then set up a QT for the injured one. You can also start looking around to see if anyone will take two of the three now and then the third when she's healed up.

 

[Paradise3]

Have you got a spare tank lying around? I'm thinking you need to remove the other flags, then set up a QT for the injured one. You can also start looking around to see if anyone will take two of the three now and then the third when she's healed up.

 
I do, but only the one and no room to set it up currently It's actually the one my fiancé took apart to sell! He still hasn't sold it so all of this could have been avoided had he waited till he sold the fish before breaking it down  
 
As for the second idea, I had thought of that so was planning to put something up in a few fish groups on facebook and possibly other sites just to see...

 

[Munroco]

http/www.ebay.co.uk/itm/5-x-28L-28-Litre-Underbed-Under-Bed-Plastic-Clear-Storage-Box-Container-Lid-SALE-/251679215455?pt=UK_Storage&hash=item3a99400f5f, something like this can easily be used for a QT for smaller fish. Can be used for other things too, like growing on small numbers of fry, or for the original purpose of storing things. You get them in lots of different sizes.

 

[Paradise3]

http/www.ebay.co.uk/itm/5-x-28L-28-Litre-Underbed-Under-Bed-Plastic-Clear-Storage-Box-Container-Lid-SALE-/251679215455?pt=UK_Storage&hash=item3a99400f5f, something like this can easily be used for a QT for smaller fish. Can be used for other things too, like growing on small numbers of fry, or for the original purpose of storing things. You get them in lots of different sizes.

 
I know, I used to breed Betta's in them. However, I do not have the room to set it up At all... The only way possible would be to get a smaller version(16-18ltr) and put it ON the Leopard Gecko rack, hope the heat mats which are set at 30c will at least take it up to 26c and no filter as I have no-where to plug the filter or heater in right now.

 

[star4]

The flag fish can go down to 18C so if the tank is in the house you may not need a heater if your house is warm enough. I have an unheated tank at the moment and that is staying at 20c.

 

[Paradise3]

The flag fish can go down to 18C so if the tank is in the house you may not need a heater if your house is warm enough. I have an unheated tank at the moment and that is staying at 20c.

 
Our room is warm so that's possible, and it would be on the rack so would have some heat. Simply because it's the only place I can possibly put it. The problem is no filter so would be doing daily waterchanges which would just stress her wouldn't it? She hates waterchange day and I only do them weekly at the minute not daily

 
Wouldn't be a tank though, would have to be a plastic storage box.