Guppy Fry strange lump! Dont wanna wipe colony!

[Vengified]

As title states, guppy developed strange lump on chest/stomach area, ONLY on the right side, the left side looks perfectly fine. The only thing they have had to eat today, is finely powdered flake food, or whatever they scavenged off substrate. Only one to exhibit symptom. Have secluded her, as to not wipe entire tank. She is 5 weeks old. Only additions to tank are the plants/fry from the 20g tank, which hasn't had any related issues recently.

Tank is 10g, fully cycled, 0/0 ammonia/nitrite, 10 nitrate. Water change 50% last night. Stocked with approximately 70 guppy fry (she is 5 weeks old, two others as well, the other 67 are only 6 days old, I know too many, but didnt expect mom to drop 100+ fry!) Also have some in 20g tank, no issues in that tank.

Attached are pictures, please, if you know what it is, enlighten me! And if you also know a resolution, please help! I would let her be, or euthanize, but I hate needless killing, and I have promised many of the other babies for someone to raise, as opposed to offers for feeder fish.

 

[Vengified]

***UPDATE***
I believe it was just stuck food, maybe slight constipation, just super evident on the tiny little body. After having her in a small container for a couple hours, and VERY thorough inspection, the strange lump is gone, and plenty of poo on bottom of container, normal poo. So she is back in with her kind. I guess I'm just a guppy fry noob!​

 

[Colin_T]

She had to go potty and you isolated her so she didn't have to go in front of the others. You are very nice to your fish