If Cosmetic Surgery is a sin what about a Tummy tuck?

One of my friends is a Christian and she recently got a tummy tuck surgery because she wanted to have that hourglass body quicker, before she got it and was considering one I argued with her that type of surgery was a sin considering she had vanity purposes but she argued back tummy tuck was just a surgery to remove excess fat and she wasn’t changing anything about “Gods creation”. but now that she’s got it I’m wondering if she was technically right since Tummy tuck is just a surgery to remove fat and doesn’t really alter your appearance or the way god made you