You can never predict how much loose skin you end up with. Too many factors influence the end result even with siblings. Then the next questions your sister might ask herself are: Does the loose skin impede you - from doing every day tasks or being more active? Does it make dressing difficult - have to go up sizes, clothes don’t fit well, can’t hide it easily, etc.? Do you have rashes or infections? Does it affect how you see yourself, confidence, etc.?
I have some loose skin, not a lot. It doesn’t restrict my activity. It doesn’t limit my clothing choices & I can dress easily to cover it. It hasn’t affected my self confidence either. So for me I didn’t think it necessary to consider skin removal surgery. It’s very much a personal decision.