Being practically minded, I would suggest that you do the following:

1) make sure she gets prenatal care, takes prenatal vitamins with at least 800 mcg of folate daily, and has a psychiatrist who would talk to her prenatal care providers (doctors, midwives, nurse practitioners - whoever they are).

2) File a police report with her to help her get rid of the stalker.

3) Spend time with her doing fun things - shopping for layette if that is affordable or just having a walk followed by a lunch

4) Unless she takes a medication that would be secreted into breastmilk, put her in touch with the local chapter of La Leche League International. I am sure La Leche league group leaders would be kind enough and responsible enough to sponsor her, both as a woman who has been abandoned by her immediate family and the father of the baby, and a person who needs extra care and support due to mental illness

5) Share your own experiences with mental illness and maybe some tips on how to deal with depression (part of bipolar in most cases) and anxiety (still part of bipolar in many cases). She will appreciate learning that she is not alone and that one can be successful despite mental illness.