If you know whats causing your mom's condition, having someone who understands and can be supportive at a time like this can go a long way to helping victims of a NB, cope with the mental anguish.
Like a man standing on the ledge threatening to jump, the right words can talk her out of her feelings of low self-esteem and self loathing.
These are two of the major factors in a Nervous Breakdowns.
Just be there for her, and be prepared for a bumpy ride. The ups and downs are like an emotional roller coaster.
But the hollow feeling in her stomach will decrease as time passes, and soon you will see her start to regain her self.
Above all ask questions and be a good listener. Help her get all the hurt out. Encourage her to cry
At night sleep in the same bed and hold her it may sound odd but it will remind her of being wrapped in her mothers arms, the safest place for a tortured soul.
If you remember how it works for you, well it will do the same for her, and the thought of you being there for her, in such a meaningful way will help her recover that much faster.
Just showing her that she is loved, and the degree of your love and concern will be great therapy.