What a challenging subject this is. I have been many shapes and sizes, and when I was in high school, I hit maybe 240 lb of chub, and as a result have had a fair amount of loose low belly skin since losing the fat. Anecdotally, for me, intermittent fasting & a mostly organic diet seemed to work well (although, admittedly this is speculation). I am 45 and in the last year or so my skin has tightened up. I do use suppliments targeting senescent cells (NMN, apigenin, spermadine and a few others sometimes) which my be part of it. Also, my wife had loose belly skin from our 1 child (birthed 12 years ago) and has managed to significantly tighten her belly this year as well, with some diet changes and exercise. I honestly thought it would only get worse with time but we have both experienced positive changes. Surgery is a personal decision of course, with it's own series of complications and benefits.

My wife is a tiny woman, she is 5"3' tall and she weighs 125LBS. After having three of my children she has a lot of loose skin on her belly. She is very self conscious about it and has decided to do the surgery. Yes, it is very expensive, $12,000 + expensive. Surgery is the only way to get rid of that loose skin. I would say, save your money and don't go cheap on the surgery; cheap surgery can make things worse. What I'm about to say may sound corny, but, Just assure her you love her the way she is and tell her she is hot. If it is a big issue for you, have her wear a corset, it hides quite a bit of skin. There is no magic pill, there is no way around loose skin other than surgery.

Honestly brother for me it had a lot to do with age. High school I ballooned up for offensive line, but in college dropped 105+ and switched to TE. I was lucky enough to mostly tighten back up despite a few stretch marks and 0.25-0.5” of extra skin below my belly button. I tried topicals, target workouts, diets, gh, etc. I have yet to find anything as effective as surgery. Had a buddy who lost 150+ and his stomach skin looks better than mine besides the scarring which is minimal. If she’s back in shape and it’s truly skin I would probably say the same. Best of luck to y’all- keep in mind I am by no means an expert just another guy!