Pardon me for not knowing the difference, but if it is a female, it could be uterine prolapse. For that problem, I am more familiar with Guppies, but they can live with it, if there isn't a place it seems to get infected, like a split or open wound. The water quality is very important for helping to prolong their living with it. I have read that some have put it back, though I wouldn't even think of how one could do that. Never actually heard of someone I know of doing it.
10 years old fish, is a good long time. It is really hard when you have a fish which has been around and or/with you for so long and has a serious medical issue. I am sorry your fish is unwell and hope someone has some better help for you.