AITA for skipping Mother’s Day after what my MIL said to me?

My MIL (“Karen”) and I (30F) have never had a good relationship. From the start, she’s believed I “baby-trapped” her son when I got pregnant during COVID. There’s been years of tension and passive-aggressive comments, but I’ve always kept it respectful and treated her like family anyway.

Apparently, that wasn’t enough.

Last weekend, we were visiting her and my FIL (“David”). While we were outside, she casually walks up to me and says:

“I told David the other day that we can finally accept you as part of the family.”

I genuinely thought she was joking. I’ve been with her son for 7 years and I’ve been raising her grandchild for 5… but now I’m finally “accepted”?

Then she explains why:

“It’s official now because I realized—after my son told me—you’ve been paying all the bills since he lost his job.”

So, just to be clear—I wasn’t family when I had her grandchild. I wasn’t family after 7 years.
But I am family now that I’m financially supporting her son?

I laughed it off in the moment because honestly, what do you even say to that? But the more I think about it, the worse it feels.

For context: yes, I’ve been covering all our expenses for the past 3 months while my partner is unemployed. But I’ve always treated them like family—long before that.

Now Mother’s Day is coming up, and I really don’t want to go. My partner says I’m overreacting and literally laughed when I told him what she said.

So now I’m stuck wondering—am I the problem for wanting to skip it?

Or am I justified in not celebrating someone who only sees me as “family” when I’m useful?