I think that given your partner has had health problems in this arena lately, the very best thing to do would be for her to check in with her healthcare provider and ask if it's okay, and if not, when it will be okay. It *probably* us because the bowels are not something anal sex tends to impact (no pun intended), but I'd still check.
I'd also figure that if it is okay, she (and you) might want to be prepared that it's possible it might cue some trauma for her. In other words, that kind of contact could remind her of any part of this and wind up being something she needs or wants to stop very fast, and might need some emotional aftercare around. Butts and that arena tend to be a place of the body where we all -- pardon me if this sounds hokey -- store a lot of emotional stuff, so it can already be something extra-vulnerable with sex, all the more so if someone has had any kind of physical pain or other trauma in or around the area.
Never doubt that a small group of thoughtful, committed citizens can change the world. Indeed, it is the only thing that ever has. - Margaret Mead