Please Help!

Please help! I have a beautiful 8" long pangasius who I've had for three years. She is my pride and joy and the first thing people notice when they walk in to my house.
 
Lately she has been getting a little bit podgy looking (I just thought it was the fact that my boyfriend likes to hand feed them and has been indulging them a little too much because there are two or three looking like little porkers at the minute and she seems to gobble food up like she's never seen it before!) but after getting home from work today one side in particular is incredibly swollen and she has a small round wound (about 3mm in diameter) which looks like a huge boil with puss or some kind of tissue coming out of it.
 
I'm really scared and have no idea what to do to fix it. She's only had a small (2" long) pictus catfish added to her tank recently so I can't think of what it could be.
 
I have a 2ft quarantine tank but am unsure as to whether that will be enough for her.
 
Any help would be appreciated
 
P.S. 
Her tank is, for now, 240l and she has lived with the current tank mates all her life. I know her tank won't keep her going for much longer and I'm in the process of getting her a 600l tank set up.

Can you post a photo of it?
I feel like the QT will be big enough for now. It's not a long term solution. However, clearly it's important to keep the water expertly clean in it.

I would suspect some sort of bacterial infection; most pus-y spots are. Myxazin is what I rely on for those kinds of problems.

 
My apologies for the quality of the picture, she's camera shy and insanely quick!
 
Have put myxazin in the water (the first thing my dad did, think he's worried too!)
 

I wouldn't completely discount the hand feeding as a possible connection. Overfeeding can cause issues and unwashed hands can spread bacteria.
 
I think antibacterial treatment is the correct course with more frequent fasting. Not too much of course but I would cut back a tad on the feeding just in case it needs to digest.

I really hate trying to diagnose remotely based on a description. I can not tell much from that picture. All the research I did pointed to things not good. There is no guarantee at all these may even be a correct diagnosis, but at least have a look and go from there. Glugea and Henneguya
 
Also for sure do a Google for "Glugea and Henneguya" their are a lot of images too.
 
I am probably way off the mark, but I would have rather you consider the above and decide it is not this than not consider it and have it be. I agree about moving it into a separate tank. Smaller is also cheaper to treat. Provide plenty of air, change lots of water.
 
A better bet would be to try and find a university with an ichthyology dept. that might help or even a high quality LFS.

I hope she gets better soon. I would also like to point out that she needs a bigger tank than a 600l, in the wild, this species grows to nearly 1½metres. In captivity, they will normally go to around 1metre. The danger with keeping her in a tank that is too small is that she may become stunted, and live a painful existence. Have a quick look at the blue link in my signature.

It's important, I think, to point out that when we use the word stunted we don't simply mean that it doesn't grow as large as it would in the wild, it actually includes spinal deformations which can lead to many other problems including interfering with organ function.

I do know all about how big she will get and the damage that will be done to her internally if she is kept in inadequate conditions, but as I'm currently studying for my degree I can only afford upgrade her tank as she outgrows the one she is in. However I am perfectly aware of my responsibilities to make sure she's perfectly healthy and happy. Just want to point that one out!
 
Thanks for your advice. I'll be sure to keep people up to date