Hello flower: I noticed this is your first post here on PC. So... welcome to Psych Central.
I don't know a lot about BPD myself. Perhaps other members, here on PC, will have some thoughts with regard to your concern. Based on what little I do know, though, I'm inclined to doubt there is any direct relationship between not wanting to have a job & BPD. (Perhaps I'm wrong about that & other members will correct me.) On the other hand, I would guess a person who has been diagnosed as having BPD could decide they don't want to work just like anyone else. Impulsiveness & emotional instability, as well as anger, are considered to be among the symptoms of BPD. Perhaps what your mother has decided in terms of her employment status is related to that.
You asked if anyone has any advice to offer & I don't know as I do other than to say that, at least from my perspective, your first responsibility is to your baby & to yourself. You can't force your mother to make good decisions. At some point I think she simply has to suffer the consequences of her actions. You wrote that you know she feels as though you are abandoning her. And that is more than likely the case since fear of abandonment is a hallmark of BPD.
Here are links to 5 articles, from Psych Central's archives, that (hopefully) may be of some help with this, the first 2 by our host Dr. John Grohol, Psy.D.:
Borderline Personality Disorder
Frequently Asked Questions about Borderline
How to Help a Loved One with Borderline Personality Disorder, Part 1
How to Help a Loved One with Borderline Personality Disorder, Part 2
Dialectical Behavior Therapy in the Treatment of Borderline Personality Disorder
I hope you find PC to be of benefit.