Mori

While it was confirmed that it's part of their powers, I don't recall it ever being specified exactly how it works for Jane.

Rita is a shapeshifting rubber blob that just doesn't age, Larry is being kept alive by the negative spirit, Cliff's brain is preserved in his robot body, but Jane's version of immortality is less clear. Each of her personalities has different body chemistry, so it could be that every time she transforms into another personality her body resets to the way she was when she first got her powers.