She is just uncomfortable. My cat did this. It could still be a few days. Go with the flow!
I'm afraid I would have said something. Like "Excuse me, this is MY conversation, with My friend. Right now I don't need your overbearing opinion an a private subject. But if you'll give me your phone number, then I will call you for your opinion on a subject you know nothing about".It's best you did not get into an argument with her. I think it is everyone's own personal decision and must be based on numerous factors.
I do not advocate terminating past the halfway point. It can be very difficult for the mom physically and emotionally. I also think that no one should judge another's decision either way.