You stood by and let another woman plan YOUR daughter's wedding and now you're the unreasonable one... that's a load of hooey.
BTW I LOVE that hunny pot idea. That is TOO cute, and something that can be used again later to continue the fun... awesome.
Maybe the MIL is afraid that she'll end up being outshined? Just the couple bits you've mentioned it sounds like you're an awesome party planner... first she's outshined by your daughter... her son 'abandoned' her to marry the girl... now his new 'mom' is planning this awesome party for 'his' baby... could be some serious insecurity issues.
What about a Father In Law? You haven't mentioned that... does your DD have one? Or is MIL a widow? or Divorced? That could also add to the makeup. If it's only been Mom and Son for many years... oh man, then you add codependency too...
Sounds to me like you are being loving and supportive of your daughter and I think that's the absolute best thing you can do, especially since it sounds like she's really going to need that support system.