20 year anniversary - spouse wants to attend a wedding instead

Our 20 year anniversary is in May. My spouse and I had previously discussed finally taking an extravagant trip together, like hopping some islands in the Mediterranean. Then a few months ago one of her cousins announced her wedding date a day before our anniversary date as our anniversary (occurring on the other side of the country, 4ish hours drive from an airport) and my partner went silent. I made it clear that I wanted to stick to our plans and finally take an overseas trip together that week. More silence, for months.

As backdrop, we've been in marriage counseling twice due to (partly) my wife prioritizing friends and family over our marriage. She would cancel our plans if a friend was coming to town or her parents wanted to do something else, and she would postpone making summer plans until she could first confirm what her friends and family were doing. It got to the point were we hadn't taken a couples trip for 5+ years and I was saddened by this. I'd tried to make plans but she always complained she was too busy to take time off work, but would drop everything for a girl's trip or to travel with her parents.

She's also never been great about celebrating my birthday or father's day.

Marriage counseling was rough but productive. The therapist explained to my wife that it's important to prioritize your marriage and ensure that each partner works to fill the other's cup. My wife said she understood and vowed to change. But we still haven't taken an overseas trip, and that was three years ago.

When I followed up last week my wife about her silence regarding our anniversary trip, she said she had avoided talking about our anniversary trip because she hoped I "would just eventually decide to come to the wedding."

For context, this is a cousin that has never visited us, they don't call each other on birthdays or on holidays etc. We all get along but it's very superficial. They are not close.

I'm not taking it well. I'm hurt and feel like it my wife can't make our 20 year a priority then there isn't much chance of things ever changing. And trying to argue with someone to convince them to want to go away with you and celebrate feels pretty darn depressing at this stage in our marriage.

Am I overreacting? Or is it reasonable to be upset about this and questioning our future together?

Edit: I'm aware we could do both, or celebrate at a different date. The issue is that my wife has already decided to spend the entire week with her family. And she hasn't proposed a compromise. In therapy we agreed it's her job to repair if she cancels again. She has not proposed an earlier or later trip or any type of compromise.