Hi Meg and welcome. I had a very similar situation with one of my kids. They were married a few years back to a non-JW. My son was never baptized, so he was not "officially" a JW. My ex-wife is still a hard-core JW and would not come to the wedding claiming she had prior plans! Though he was hurt by his mother's decision, he realized that the day would be much more joyous without her disapproving presence dampening the day. Interestingly, other JW family members did attend and had a great time. (the wedding was not held at a church)
Selfish, cult-like behavior extends to most areas of life...this is the same woman that did not attend any of her children's graduations from university because "that type of education is not important".
Enjoy the day with your daughter...her father will ultimately be the one hurting himself by his decision.