I think you are absolutely being reasonable to expect that she attend. As your partner she should be happy to do so. If you are making plans then she should be modeling her role in that family and that includes supporting you and your daughter. I don't think it is an accident when you have been so flexible. I think this is an example of how selfish she is (sorry). This is very self serving to avoid your daughter's party. This is a glimpse of how supportive she will be in the future unless something changes. If she can't compromise she can't be a couple. A deal breaker is being there for each other. You should consider that she is not only physically absent but is also emotionally absent.
Please press accept; this is the only way I am compensated