I'm in an awkward situation. Last week the mum of a friend of DS (7) said would DS like to come to her son's party which would be at an animal farm. I said that it sounded lovely, thanks but DS is going away with his father so could she tell me when the party is. She then said that she had already bought the tickets on Groupon and she could make it at a time to suit and that actually, she was only inviting my DS. So I said OK then. Then she said but the thing is that it is in Sunny Town which is 1.5 hours away from where we live. So I said I would take him (although I was finding it strange by this point). She then asked if I could also drive her and her DS there as she would no longer have her car by then. By this time I was uneasy but she had caught me on the hop so I said OK. I then decided that this was not practical and, in addition, I didn't want to have a day out with her as, for reasons I will explain below, I don't want to encourage a friendship with this lady. I gave her an excuse and said that actually, we couldn't come. She gave me a solution to my excuse, so I said the solution wouldn't work for me, then she thought of another solution and I responded that I still couldn't go. I thought that this was the end of it and now she has thought of another solution which I cannot think of an answer to (basically, she would get someone else who I don't know to drive her, her DS and my DS to the farm). I haven't replied to the message.
The thing is that I do not want my DS to go. She has a very chaotic life involving domestic violence and serious mental health problems. She lost custody of her eldest daughter a long time ago and the father of her son is in and out of prison. She seems to really want her son to be my DS's friend because her son has few friends due to some kind of social communication problem. I don't mind my DS playing with hers but this lady is paranoid and I don't want to be dragged into her paranoid delusions and I feel that she is latching on to me. We have absolutely nothing in common apart from the fact that our children go to the same school. Neither do I want my DS involved in their chaotic life. She has her good points but she has "trouble" all over her. She dislikes all the other mums at school and calls them and their children evil. She put on Facebook that she was hearing voices again (not sure if that was a joke or serious).
How do I deal with this situation? I think I've made enough excuses about this trip but she keeps persisting with solutions. I can hardly say that I just don't want him to go can I? I won't let him go so how do I handle it?