Without knowing what she got pre or post surgery but knowing she's on nothing now, I'm sure she's uncomfortable! I'm not familiar with any allergic reactions to pain meds in rabbits. The old school train of thought with animals was that it was good to keep them in pain so they wouldn't run too much and tear their sutures out but now we're more along the lines of stronger pain meds and confining them better.
If she's eating and drinking it's not urgent and I wouldn't risk giving her any over the counter human meds, but in the future I'd suggest pain meds. Generally the thought is unless we know for a fact it doesn't hurt animals, assume it hurts them just as much as it hurts people.
If she's just pooping everywhere but peeing in the box she may be trying to mark her territory since someone kidnapped her away from it.