Would having a tummy tuck surgery bar someone from rejoining after a break in service?

No. It's a cosmetic procedure done for aesthetics. As long as the person can still perform the range of motion, PT etc., then it would not be an issue. If anything it would help as it takes away some of that tissue that would have been measured in a tape.

As long as it doesn’t prevent her from performing her duties and responsibilities, especially PT, then she’ll be fine. Good luck to you, I hope this helps...

It shouldn't as long as she doesn't have any service limiting conditions. Make sure your "friend" also has documentation from a doctor stating that there is nothing abnormal about the healing process nor do they have any restrictions in daily life. That will assist when the recruiter and MEPS when they go through the medical packet. One less step your friend has to take.