I am wondering how you are getting on with everything? I have had a very similar experience with my mother, she was in and out of psychiatric wards when I was a teenager and I ended up having a nervous breakdown and four months of treatment in a psychiatric unit myself. Things were so bad I took an overdose and used to cut myself regularly with pieces of ripped up coke cans. When I got myself together I moved 200 miles away and went to university, did very well there (1st class hons!!) despite having got low grades in my A-Levels (though I was lucky to get any A-Levels to be honest with all that going on).
We've had a very difficult relationship for a number of years as I find it very difficult to forgive and forget and she will not say sorry or take any responsibility for what happened to me when I was a dependant.
Her version of events is that I was a difficult teenager who pushed her over the edge. (I was a straight A student who didn't drink, smoke or have boyfriends!!) Also she used to blame me for the breakdown of her marriage (it went sour when they had a baby after 13 years of happy marriage) etc.
When I had my own baby last year things were very hard for me as I could not understand how my mum had said those things to me as I would not say anything like that to my baby. However as time progressed and I got tired and depressed at being a new mum and my partner and I were rowing a lot I did get a greater understanding of her feelings and situation.
We have now reached a mid-ground where I see her for a few hours every couple of weeks (we live about an hour apart now). She has actually turned out to be a good grandma and my little boy loves her and loves spending time with her, which has helped my relationship with her.
I have realised that a lot of the shitty things she has said to me over the years is because she has trouble expressing emotions in the correct way so for example when she was worried about me when I was pregnant it would come out as a comment about my weight, rather than just asking if I was eating properly etc.
However I've also realised that if she goes unchecked she will get away with murder so I don't let her get away with stuff like I used to. I try not to do this in an aggressive way but rather in a jokey way to diffuse any potential row and not to end up in a slanging match as I have done for years previously. This works well and means that I don't get upset and also that she gets to spend time with her grandson and him with her.
Your mum would not be coming all that way to see you if she didn't care about you. She may not know how to get along with you in an appropriate way once she does get there, but that is the part you both have to work on.
Shutting her out completely wouldn't work, in my opinion, as you will just have to live with the guilt. Better to try to find some middle ground. I usually meet my mum in town and go for a nice meal then she can't criticise the state of the house etc
I hope you manage to get some NHS counselling as it is generally very good these days and hope you manage to find some middle ground with your mum. Best of luck.