Something hurt coming out (or going in) and she's now reacting like a normal human --she doesn't want the pain again.
It would probably be helpful to stop talking about it, and let her work it out in her own head. When she groans, you can ask her what hurts, wonder what she might do about that, or stroke her arm or massage her shoulders in sympathy... but try to avoid focusing her attention on her bum and what it does.
Feed her things that are hard to keep in: lots of water, fruit, berries, actual whole wheat bread (been seeing a lot of 'whole wheat bread' labels lately that the first ingredient is white flour), beans, peas, nuts, seeds and fat/oil.
Avoid things that make the problem worse: cheese, milk, rice, meat, corn, popcorn, sweetened drinks and juice (except prune juice, which you may not be able to get her to drink, anyhow).