In not wanting a close friendship with this woman?

[Alfieisnoisy]

So....my son attends a special school and in his class is another boy a year older.
Other boy's Mum has latched onto me which I don't mind as I am pretty happy to chat to most people. However the are some issues
Firstly I have real difficulties socialising on a 1-1 basis. I suspect that I am also on the autistic spectrum as is DS so I find this difficult.
Secondly this woman tells me the ins and outs of a ducks bum....I know everything about her family including wider family. The kind of stuff that your wouldnt ordinarily drop into casual conversation. I strongly suspect she is also on th autistic spectrum but may be wrong about that. She does have Bi Polar disorder and I know this is very debilitating for her. For example she isn't allowed to drive due to her medication etc.
I am trying hard to be friendly but also to keep her at arms length because quite honestly I find her exhausting. However I also feel that she is very isolated so I have tried to include her in local support groups I attend etc. She says this is helpful as she doesn't otherwise leave the house which I know isn't good for her mental health.
She rings me most days and if I pick up the phone she is on for nearly an hour at a time ...nothing major...just chit chat and every day stuff. I am having to ignore her calls some days as I just cannot cope with it. That may be my own issues coming into play though.

Today I took her to a group we both attend in a nearby town . On the way there she had a can of Fanta she was drinking. As we pulled into the car park she literally just tossed it from the car onto the grass verge..
I was so shocked I didn't know what to say or do so I said nothing but am now panicking about when we go again to the group in case it happens next time as well. What do I do? Take a carrier bag for rubbish? I am happy to do that. Thing is that I have never ever just thrown rubbish from a car ..not ever. Am shocked she did it and thought it was okay...in fact she said "whoops naughty me" just after she did it so she obviously knows it is wrong.

My gut feeling around her is that I just want to get away but I also don't want to just abandon her. When all is said and done she is an isolated person with serious mental health issues. I am the only person around apart from her husband (who works long hours) that can get her out of the house during the day. I feel a certain obligation to offer her some support in getting to things she wouldn't otherwise be able to access.

Is it okay to just limit things?

If I spend a period of time with her on one day for whatever reason then I ignore calls from her for a day afterwards to preserve my own energy.

Her son and his two little sisters are lovely kids and she is a lovely Mum to them. She says it is hard but she does a great job from what I can see. I am happy to get our kids together some weekends . I am happy to see her once a week and also to take a couple of phone calls but I just cannot cope with it everyday. I really can't....and then I start feeling guilty which I shouldn't I know.