I always wonder. What if the grandma got pregnant? Would the clock reset itself? Or would her time get transferred to grandpa? Since even in his old age, the grandpa can still be sexually active (remember him going to the bathroom almost every night? Yea...) while the grandma can't--most probably either due to old age or menopause affects horniness.
Because her sickness disappeared when she turned back to young again, I assumed that her internal organs followed, including her ovaries.