how should i respond...

Awww boredom, you are such a good DIL and mother. Always take the highroad, don't stoop down to her level, and don't think people don't know who's righ and who's wrong. Neighbor's/community people know what's going on better then anyone else. People recognize jaahils like they recognize night and day.

You'll be rewarded Inshaallah, and take comfort in the fact pretty soon your MIL will be old and feeble, and then won't be saying stuff to you. So just be patient. It's the Islamic thing to do. It's just a matter of time.