My mother woke up one day post-menopausal, no symptoms at all at 49. I had my last period at 55, and had severe mood swings and moderate hot flashes. I did think I was going crazy. Tell your mother that it will pass and she will feel normal again, but see her gyno to see if they can help her. I think you can reasonably expect to experience what your mother does, but it does not always apply. My MD gave me prozac at one point to help with mood, etc, but I didn't like taking it.

When you get to your mid 40s, be sure to let your gyno know about your mood issues and how meno affected your mother. Maybe you can head off the worst symptoms.