S.S.
I am bipolar, my grandmother (raised me) was bipolar, my niece is bipolar - and your mom is MANIPULATING YOU.
Sorry - that's just the way it is.
Medicine helps but the big thing is people have to control their mouths and their choices - manic episodes make it easier to say and do the wrong thing - but they don't make it impossible to do the right thing either, KWIM?
I would bring my siblings into giving mom an allowance, if you think it's so important to continue this relationship. On the other hand - I spoke to Mama only once a week, for 30 minutes - and I didn't give her money, nor do I ask anyone else for money. I have repeatedly advised my sister to stop giving my niece money - but she "Can't cut off her BABY"... even though she is raising this girl's kids because she walked out and didn't come back. I had problems with this when I was younger, but now I am maniacal about my money - I refuse to carry credit cards because of the impulsive shopping, and save receipts for three weeks - so I can bring it back when I'm sane.
Spending (compulsive spending) is an addiction like alcohol or drugs - something that most bipolar people seem to have problems with. Enabling that is just like buying her crack.
S.