And she'll have to do all this before she hits the age where women really do become menopausal.
You only reach menopause if your body actually changes. I could get into the biology of it, but I doubt anybody wants to hear it. Suffice it to say, as long as Leah does not age, no matter how old she technically is, she will physically remain however old she was when she started phasing. Meaning that if and when she decides to stop phasing, she will start at the physical age of 18, or however old she was, and then move on from there.