You don't get to tell your MIL how she gets to feel about all of this. She is a grown woman, and will make her own decisions about what she wants to say to her daughter, etc. Don't try to control that; neither encourage her nor discourage her to say anything particular to your wife.
Did you agree to meet your wife on Monday? I'd strongly suggest that you not, or at least say "Monday doesn't work for me. I'll be back in touch soon and perhaps we can talk some more." Don't be at her beckon call.
