A few items can be used to prevent falls from bed including a bed rail or pressure mounted floor to ceiling pole beside the bed and a bedside commode so your mother does not have to get to the bathroom in the night.
Once she has fallen, the recommendation for getting up is:
1) take a minute to make sure she isn't seriously hurt
2) attempt to get onto her side
3) move onto all fours in a crawling position
4) crawl over to a nearby chair, with arms preferred
5) get her forearms up on the chair
6) shift her arms towards one side of the chair while moving her bottom up and, hopefully, onto the chair surface
7) sit back into the chair and rest until she feels strong enough to return to bed
Doing all these steps slowly, even over an hour, is best.