Issues relating to my natural mother...(long)?

I know I don't always see eye to eye with the adoption section here on yahoo answers, but you are smart folks who I thought might have some insight into this problem. I am in reunion with my birth mother, lets call her Jane. I was adopted first by my grandparents when I was born while Jane went across country for whatever reason, and upon their death when I was still very young by extended family. Without telling a story that goes on for days there was some friction prior to and after my second adoption where Jane could not be found, and then showed up more then a year later and made some unfortunate choices. My adoptive parents didn't always make the best choices either, but allowed contact by phone and letter. They did not allow unsupervised visits due to some concerns they had. Jane disappeared from my life, reappeared when I was about 17, disappeared after telling me that she was too bitter and angry about the past to be good for me (my letters were returned, her phone number changed) and then reappeared about 10 years later. I am glad to be in contact with her, but find it very stressful. I feel obligated to stay in contact and give her the benefit of the doubt and so on... but she lies to me. I wasn't a baby when she was dodging in and out of my life, I was about 5-7 and then 17. I remember things. Not things I was told, but things I overheard or saw. She bad mouths not only my adopted family but other, shared family members who have always been good to me. She refuses to take responsibility for not being in my life, even though at best it was only difficult not impossible (if she called after midnight my adoptive parents wouldn't wake me up for the call, they wouldn't let her fly me across country to spend time with her because of the times they weren't able locate her) She asks things like "is so and so your real family, or part of your adoptive dad's family?". She breaks her word with me, and lets me down. She makes plans to meet with me, and then cancels at the last minute (I haven't seen her in over 20 years). She seems to think that family members who didn't bother to stay in contact with me after I was adopted (despite going to the same church, or them knowing where I was the past 20 years) should be more important to me then my adoptive family. I've tried addressing things head on, but it goes nowhere. I tried just ignoring it when she gets hateful about my other family members, but she keeps it up. Its to the point where I don't trust what she says, and I resent her meddling in my other relationships, but I feel obligated to have her in my life. Anyone have any suggestions on how to deal with this? My adoptive parents haven't said a bad word about her in about 15 years, and they support our contact. Anyone have any insight into why she acts this way, and how I can address it without being hurtful? Or should I just give up? Do I expect to much?