If she does show up, I would send her to a motel. Come for a visit, fine, it's time to leave, here's a hotel room at blank, you can come back to visit tomorrow after lunch (just and example).
My first cousin's mom is schizop, she follows him everywhere all growing up after the laws changed and she could release herself from the institution. She won't take meds, so she is how she is. She moved every time he moved and she lived a few streets over until his wife made them buy a condo in a gated community. She would stop by daily, many time a day and bring him donuts from the shop she worked at.
It started for her after my cousin was born. Prior to his birth she had lost a baby boy when he was 2 months old from SIDs, I just learned this in the last 2 years (they were both smokers in the 60s btw). To me the lost of a child is enough to send someone over the edge regardless of their prior mental status. My uncle learned later that she had signs of schizop in her teen years but no one told him when they were dating. I had no idea my poor Uncle had been through so much, he never did re-marry and he raised my cousin on his own with the help of my grandparents.
My cousin's wife was really worrying the family a few years back b/c he was having paranoid dellusions that the gov't was out to get him and watching him. When I've seen him, which is rare due to the live so far away, he does not seem fine. We were a bit mifted as schizop usually developes in someone's twenties or it isn't going to develop -- my cousin at the time was in his mid to late thirties. My mother has not heard anymore about this since 2004 that I know of. His wife will not have children, partly due to the mental illness factor and partly b/c she has enough nieces and nephews from her many siblings she just seems content with that. My cousin really wanted children, she is older than he is and it's too late for her to change her mind -- sad.
I just wanted to give you some hugs and support. If your mom's entire family is suffering from mental illness, you need to take care of yourself and be sure someone is watching out for you -- many mental illnesses are genetically linked. And getting help early can many people lead perfectly normal lives, I know a few people who are schizop on meds and lead normal lives now, but dx was hard to get b/c as teens many thought they were on drugs even their parents.
It is hard to tell family, especially your mom, to stay away. I don't think there is an easy way to do it and she may not even hear you if you do given her state. I'm surprise there are no social workers for her in the state anymore, that just seems so wrong. Someone needs to be looking out for the well-being of adults who are mentally impared by mental illness. Especially when her siblings are in the same state of mental illnesses all around.
I don't think giving her access to your Fed Ex acct is wise, she could go manic and mail stuff all over the world, depending on what sort of manic person she becomes.
I don't think there is an easy answer. You love her, but she really can't be around you right now as she is toxic to you.