My Molly is looking strange

[Andrew Beard]

I have a wild Sailfin female Molly and she's been my best fish for a long time but unfortunately she's been having problems lately. She gave birth to 14 really big fry and ever-since she's been strange. She is getting a large red thing on her dorsal fin. It looks like a blister or something. Does anyone know what's going on?

 

[WILDER]

You will need to treat her with anti internal bacteria med, you could add some melafix as well.