We have been together one year, not "a few months ago". In your view, couples in a committed relationship shouldn't discuss these types of things prior?
A relationship can be profound in just a few months, so it’s not dismissive to be accurate (is it just me or are mustachians more than usually prone to measuring relationships in decades?) But you don’t actually seem to be connected to
her so much as the idea of being partnered (for instance, expecting top billing for the mostly arbitrary significance of a particular anniversary day... which happens to be right next to a major holiday, especially for families with children.)
You cite there’s precedent for this behavior (“keeping things to herself and telling me after the fact”) & she’s repeatedly sent clear, & frankly appropriate, signals that she has a life going on - in which you are invited to come along, or not. To me that’s a perfectly acceptable level of engagement for one year in, even for a single person without children - personally I would need to know someone well
& for them to know me well, & show enthusiastic acceptance of who I am, before I want to start orienting my family life or holiday plans around them. I’m not hearing you enthusiastically accepting her so much as casting her in a role you predefined & giving director’s notes on how you think she’s not living up to the casting.
YOU are the one for whom a relationship seems to define some kind of clear “life before” & “life after” - but that puts a whole lot of significance on a romantic tie which we often don’t in other close relationships, which isn’t how everyone else necessarily works, or needs to. If that’s distressing to you - if you feel like her life approach, which sounds like it has been consistent from when you started dating when you were theoretically attracted to it, should be transformed by your presence in it - I suggest digging honestly into why, because again, you seem far more attached to your idea of how “a relationship should look” than to the living, breathing person with whom you are theoretically trying to build this relationship.
Also, what Paper Chaser said - if the plans were discussed but no reservations made three weeks out,
for a holiday weekend, for a first anniversary you supposedly valued enough to discuss months ahead, you’re actually sending some mixed signals about YOUR commitment. I wouldn’t be surprised if she is recognizing how conflicted & uncommitted
you actually are to
her, whatever you’re telling yourself otherwise about how committed you are to your imagined ideal of who she might be
if she weren’t herself - but she’s still invited you to join if you want to go with her (the real her, the one who makes backup plans for her family for a children’s holiday, when the boyfriend thinks about making plans out loud, but doesn’t finalize them.) It sounds like she has a clearer picture of you than you do of her & is still giving you time to come around.
Kris is right & said it better & shorter. I don’t think you belong with this person because you’re unwilling to accept her. If you feel like she needs to change to have a good relationship together, that implies you think of her as an obstacle to your goal rather than the goal itself.