In short..this women sounds like a nut job and a bitch based on what you've written here. Hopefully your DH doesn't let his dick take control of his thinking brain. If she wasn't so judgemental/manipulative and aggressive about this now that she knows you don't want it, I wouldn't be so harsh.
I hope your husband is smart enough to see that temporary excitement can ruin a good relationship. I also hope he is strong enough to let you go if he is poly or just wants to have an open relationship.
"She wants to have a child with your husband????" - fuck her and not in the good way.
If some guy came over to my house and spoke to me this way (called me emotionally stunted), I'd show him how stunted I was and stuff a foot in his ass...and then I'd be single anyways because Redpepper hates that stuff