This is why I suggested that you need to talk to your husband and come to an agreement that you are BOTH comfortable with in these situations. It sounds like he wants his mother more involved and you don't. If you don't address this now it will always be a problem between the two of you. You both need to share your feelings on how to deal with MIL. You on how you want her to butt out and maybe him take a firm stand with her, and him on why he wants to give her the info in the first place.
I'm saying this from experience. I have a very difficult MIL and the first few years after I got married/had kids were hell sometimes. I just couldn't see why my husband wanted such a close relationship with such a condescending, judgemental mother. It took therapy for us to work it out after 3 years and lots of hurt feelings. Talk about it sooner rather than later.