She wasn't happy with the Lego thing, you explained your intentions, she understood. Don't read into the nice mean thing. Just take a good interaction for face value.
As far as her inviting you, I'm not going to mind read, maybe a little bit she mentioned son was bored, and her invite might have been to deal with some bored kids. Who knows.
You should answer her when she asked if you want to pop over later. Being less available doesn't mean ignore it. If you don't want to go, don't go. But tell her simply, " thanks for the offer, I'll have to pass"
