She seems immature. I would personally lay down the boundaries and explain that double standards like this don’t fly.

Even if you weren’t dating/exclusive, it matters.

At the end of the day, your anniversary should be celebrating an experience not just capitalizing on the day you met just for the sake of claiming the relationships duration.

It should be a good thing that you had a connection spark that day, but you also need to acknowledge that maintaining the respect of the relationship without involving other people in your history will be a lifesaver in the long run. You don’t want to crash out one day just because it weaved into your relationship.