Have you consulted an attorney about any of this? That just seems high to me and she should be able to work full-time or 2 part-time jobs if full-time isn't available since the kids are grown. Alimony is ideally designed to help the ex get back on his/her feet which shouldn't be too awful hard for her with no small kids around.

She could probably find a full-time job that offered insurance as well.

I agree with the above poster about setting a specific end date and including a clause about cohabitating.