I think it all depends on so many factors, it would be impossible for any of us to give you an accurate idea. What kind of procedure they will use, how severe her illness is, her general health prior to the rupture, how well she listens and follows the doctor's recommendations for a speedy recovery - these are all things that will affect how long she is down.
What does the doctor say? That's the person to ask.
p.s. May I say I'm shocked that they haven't removed the appendix already.