My (27M) partners (26F) mom (62?F) is getting too involved in our relationship

Sorry my English is not the best so I wrote in my native language then translated it.

TL;DR: Partners mother gets involved in our disagreements. Partner tells mom about every disagreement.

My partner tells her mum ("Kate") about virtually every disagreement we have, despite me repeatedly saying that I don't think it's healthy for our relationship. (I.e. her mom is going to dislike me)

My concern isn't that she talks to her mom for support. It's that her mom only hears one side of every conflict. She doesn't see the reconciliations, compromises, apologies, or the good parts of our relationship. Over time she's basically building an image of me based entirely on our worst moments.

I've also noticed that when my partner talks about other people, her perception can be very different from reality. For example, she often says that my friends don't like her, despite the fact that they're constantly asking me to invite her to events and include her. That's one of the reasons I'm concerned about how our disagreements are being presented to her mom.

This has already caused issues. At Christmas I was genuinely sick and lying down on the couch. Kate repeatedly made comments like, "Of course he doesn't want to be here, he's not family." We've been together for four years and had even lived with her parents temporarily.

The latest incident happened after my partner's birthday. I had a time-sensitive work commitment that my supervisor had organised and couldn't be moved. I left at 6am and didn't get home until 8:30pm. I wished her happy birthday before leaving and had planned to take her out for dinner later in the week because she hadn't been able to tell me what gift she wanted.

The next day I received a text from Kate saying, "Did you know it was X's birthday yesterday?" I asked my partner why her mom was texting me about this instead of her talking to me directly. That's when she told me she felt I hadn't made her feel special.

My issue isn't that she was upset. If she'd told me directly, we could have discussed it. My issue is that somehow her mom became involved before I even knew there was a problem.

Am I unreasonable for thinking that relationship issues should generally be discussed between the people in the relationship first, rather than being filtered through a parent who then starts contacting the child's partner?