How to turn down play date from a pushy parent?

I met a woman and her son at a park near our home. She seemed friendly. We exchanged numbers. Long story short my son (almost 3) does not like her son (3, nonverbal). Her son has pushed my son and doesn’t communicate. She is a recovering drug addict and to be honest not a friendship I want to cultivate (no judgement on her past just not someone whose company I enjoy). However she keeps messaging me “what u up to?” “Let’s get together” etc. I made the mistake of inviting her on a library outing. Not only did her kid hit his head and she demanded an ambulance...I had to walk home and pick her up from the hospital since she doesn’t drive. Plus she would ask me to buy her kid food when I bought food for my own. It’s my fault for being too generous. I don’t want any sort of relationship with her and my son is very adamant about how much he dislikes the kid. If my son liked the kid I would arrange play dates.We keep running into them occasionally. Thankfully my son has been nice to her kid (we have lots of talks about being nice even if you don’t like someone). But then this woman will keep messaging me nonstop. If I don’t answer she will send “?” And another “u there?” “What u up to?”Do I keep ignoring her? She doesn’t seem to get the hint. Or do I say my kid doesn’t want to play with her kid? I don’t want to be rude. I know she is a single mom living with her parents and has no job or car.TLDR: Parent I met at a local park isn’t getting the hint neither my child or I want to spend time with them. Do I ignore constant texts and Facebook messages or be direct? (If so what to say?)Edit: it’s been about 6 months of texts where I mostly don’t reply. Run into them somewhere and they start again via /r/Parenting http://bit.ly/2FKILQD