I'm hoping it is not a bacterial disease such as dropsy and there is an obvious bloat which was cause for my first question.
Several factors encourage the bacteria becoming an issue. Unhealthy water conditions such as parameters, aggression in the tank just to name a couple.
Do you know the parameters? How long have the clowns been in the same tank? You mentioned aggression between the two which could weaken the immune system. If they've not been together long and nearly the same size there could be a lengthy submission session or worse.
Please keep us updated and again, my hopes are they have just become a mated pair and she has a ton of eggs. Fingers crossed for ya.
One final question. Have you seen its poop? Normal or white and stringy?