Dealing With a Drug Abusing Mother?

My mother is addicted to drugs. She has been my whole life. My parents got divorced and now lives about an hour away from my dad, a very decent guy with morals and not a drug/alcohol abuser.
They divorced because my mother was intolerable. She has used everybody in her life to get high. Parents, husband, friends, us kids, and strangers. She has lied, stolen, bargained, begged, pleaded for money, rides, stuff whatever she can get her hands on. She is in and out of jail for “soliciting”. My mother stole from me, told me lies, took me places no child should ever go, instilled memories I should not have.
She has 6 children. 5 of whom are my fathers. The youngest, age 6, is by a guy she doesn’t know. My father cares for her as if her own. She had the baby after the separation. he has legal guardianship.
My mother is very cunning. She has a charming personality and knows how to get her way. I usually don’t speak with her except through the occasional email.
This Christmas she promised her youngest daughters, age 6 and 14, that she would come down to visit. My father went up to her house, and after searching the city for her, picked her up. But not before getting home,she got a phone call from a boyfriend. She made him turn around so she could do some “shopping”…
She missed Christmas. She was never a mother to me but the youngest do not know the damage she has inflicted. Sometimes she says she wants help, but she always go back to the streets looking for that next high. She says it’s great being sober, but I’m not sure if that’s the drugs talking, or her.
I’m not sure how to react. Do I say that this is enough? I want to believe that she can change. But I do not.
I do not feel like she is a mother. I don’t love her. She has done many hurtful things to our family and friends. I wouldn’t even giver her the time of day if she didn’t give birth to me.
People would say that I should be grateful because she is my mother… then why doesn’t she act like it? Will she ever? Would I be better if we had her out of our lives? I feel like the answer is yes, and I feel like it’s her fault anyways.
But what if she does want to change? and I’m not there to support her? I don’t know what it’s like to have a mother that is supporting of me.
Part of me says “I’m being a brat for wanting her gone. I should always support family”
The other part says “Good Riddance! She was no good anyways!”
I don;’t know what to do
She has told our family false illnesses all for the sake of money. Claimed to have had: Shingles(possible*), Lice, Scabies, Appendicitis, Diabetes, Cancer, H1N1, Lupus, and other various illnesses. All of which have “mysteriously” been cured.
It has gotten to the point where we don’t believe ANYTHING she says. Not even “I have a job” or “I bought groceries today”.
She has also been in and out of rehab for 15 years. Once, she called my sister and had her sneak pills into rehab for her. My sister was 12!!