The thing is, she is always doing stuff like this knowing how I feel. It's as if she is daring me to say something. I've spoken to my wife on other occasions about things like this but it does no good.
And from your introduction thread (posted under your previous screen name, "Sahara"):
After we got married her mother started putting the pressure on her to study with the JW's and in time, she announced to me that she would. I felt a huge crush, not knowing what to do about it because I knew how unorthodoxed the JW's were but I was still unsure what to do with myself but that just seemed like too far of a stretch ...
One by one, her father, her sister/husband and a couple of cousins fell to the JW's like dominos and I was the only hold out. Because my wife's family live out of state and all of my family and extended family are in the same county, I felt bad for her and would spend every single vacation I have ever had in the last 15 years visiting her family and going on vacations together, mostly camping. I know her family had been trying to win me over by killing me with kindness, and it almost worked.
That tells me that Mrs. Jones is probably right. I think that your wife is afraid to confront both you and your MIL, so she pushes the boundaries with you (allowing your daughter to go) and also with MIL (not going to the meeting herself). You really do need to talk this out and have clearly agreed boundaries about not proselytizing your children, or you. If your wife is not actively on board, then MIL (and aunts, uncles, cousins, etc.) will feel free to go behind your back, indoctrinating your children against your wishes. This is particularly important because of the Watchtower's antagonism against Catholics (meaning the relatives on your side of the family, according to your introduction post as "Sahara").
It really is important to get your wife on board, set boundaries, and that you both insist those boundaries be respected at all times. Failing to stand together as married partners is a huge mistake. You can't do this alone.