Her gift to you on the occasion of your marriage, OP, is the gift of knowledge. Like a wicked fairy, she has demonstrated beyond all doubt that she is not to be trusted, she will tell bare faced lies to your face and she wishes you active harm. I do not say these things lightly.
This is her gift to you, so make sure you use it wisely.
If you cannot trust her with your flowers, you certainly should not be so nonchalant as to the prospect of her harming your daughter with her nastiness. Full marks for trying OP, genuinely, but this situation is so far gone that you, and to an extent your husband, are sounding like a real wet blanket.
This stops now. Stop tolerating her behaviour.
Furthermore, since she has given you such a precious gift, I would consider it far too valuable not to share. Calmly and dispassionately, quietly ensure that all guests at the wedding are aware of her behaviour. She is a public menace.
See this as your green light not to tolerate any bad behaviour from her. I'm sorry she is like this. Good luck. x