Kayla is 54 years old and as you get older it is naturally harder to have a slim and trim body as when you were 26 years old when she first started in the business. I have to say in many cases she was a trailblazer as she was the first to undergo Dr Gerald Johnson's polypropylene string aka " silly string " back in 1998 and encouraged Minka and CC to follow her lead. Yes, difficulties followed the procedure and the FDA eventually banned it. 
I do have to say that the last photo is personally distressing to watch and she doesn't look healthy at all. 
It is shame what the passing of time can do to us. I hope the best for her.
It can not be all just chalked up to age
Christie Brinkley is 61, Elizabeth Hurley is 54, both still rocking the bikini bod.
J-lo is 50 , have you seen Demi Moore lately ?
Even some of the "big bust girls of the 90's are still rockin it. Minka, a Sarena lee last i saw were still solidly in the middle of "trophy wife/Gf territory. Lisa Lipps, last pics I saw, time has took a bit of toll, but even shje is not yet in the same zip code of "i wouldn't f--k her with your dick"
I always thought/heard that Melonie Charm was the first "silly string girl" but maybe not.
I remember reading someplace that DR. Johnson's original idea was was to make an implant shell of surgical mesh and enclose the ball of string so that as it unravels it would stop at a max size and implant it like any other silicone implant.
May have been the better way to go