Lump On Stomach/anal Fin

Hi everyone, I was hoping I could get some advice. My favourite guppy has a lump on her stomach at her analysis fin. she has managed to poop through it, it's pale, and has pale stringy bits coming off it (like a poop from after a freeze dried blood worms).
She is eating and swimming well but I don't want her to duffer unnecessarily so would euthanise her if there is no fixing the problem.
I have tried to attach the picture but the file is too large, will get on the computer to see if I can sort it out. (Doing this on my phone!)
Thanks for any help x