I am meeting my husband for lunch to discuss my MIL. Do you think he will take offense to this?

The one you should both be talking to is your MIL. I think it's time to call her to your home and both you and your husband sit her down and tell her that while her help with your newborn son is appreciated, she has more than once overstepped her boundaries and you're no longer going to tolerate it. You need to be more firm with this woman. Had that been me yesterday and she put her hands on my child after being told numerous times that you were feeding him, I would have made a scene and told her "take your hands off my child immediately. You can hold him when I tell you you can hold him or you don't need to hold him at all." Yep it's time to put her in her place.