I agree with darkeyes, your sister should get professional treatment (starting with a psychiatrist, preferably) if she isn't already. Life with bipolar/depression doesn't have to be like that. She sounds like me before I got help. Worse, actually.

If your sister IS getting professional treatment, take a careful look at it. Is a doctor waiting for meds to kick in? Okay, that takes time. But if anyone caring for her is trying to pass this off as normal or acceptable or "as good as she'll get," dump that caretaker and get someone else.

It sounds like your mom doesn't "get it." I'm glad she's there to give your nephew some (hopefully) quality care and attention, but she is probably going to make your sister's situation worse until she understands your sister is sick.

Thanks for your concern for your sister -- it sounds like she needs you!