Well,
Let me preface by saying that I understand this dynamic very well....I have just pulled my Mother 6 months ago out of a similar situation and it took me...Ready for this over 10 years!!!!
I don't agree you should "stay out of her life" after all she is your mother and it affects you when she suffers, you suffer...My main advice is to calmly (as hard as that can be) continue to speak with her and give her options like web sites (support group on line) where she can begin to see others experiencing what she is and hopefully gain some obectivity ....Suggest that she go to counseling "with you" to help "you" deal with all of this ...(A ploy of course to oepn up communication with her in a safe environment ..)
maybe her feelings will surface that can start to be looked at..find a way to start the path to gaining the strength to leave and realize that she is being abused and being abusive to herself and her loved ones.....
Make sure not to become to "obsessed" with saving her as I did at certain points, until I got help myself and became more balanced (not easy believe me

) .......If you do that , you get sick over it..not that your not anyway, but you will ....
And lastly , forgive me for appearing "religious" if you are not, but pray and have hope and faith and take one day at a time....
You say she rides to work, maybe she can be tempted to work elsewhere..Post her resume on job sites to get recruitment calls? Sounds funny but I did i that and whne other solutions came up, at first my mother rejected everything...but over time, started taking lilttle "bites" at options 'OUT" ..And finally...hopefully "success' WHen this occurs though ...get ready for the anger and the healing period......Man . it's not easy..but I kept in mind that I would rather fight the fight of "healing" than the viscious circle of trying to help her heal everytime she got upset just to stay in it and start it all over again the next week..
Good Luck and God Bless