AIO mom ghosted me on my birthday after making plans

My mom and I made plans over a week in advance to go out for dinner on my birthday. When the day came (today), she completely ignored me. She posted a generic “Happy Birthday” on Facebook, but didn’t call, didn’t respond to my texts, and didn’t acknowledge our plans at all. Basically she ghosted me all day but read my messages.

Later, I found out she drove two hours away to help her boyfriend (or ex she’s been seeing him for about three months). They had a fight over the weekend where he left marks on her arm, kicked her out of his place, broke her phone, and made her sleep in her car in –10°C weather. She showed up at my place crying, needing help and I helped her. Despite all of that, she drove 2 hours tonight to him and paid for a hotel because he was “cold.”

So spent my birthday alone. I bought my own cake, tried to celebrate by myself, and ended up crying multiple times throughout the evening.

When I later tried to explain to my mom how hurt I felt, her response was to tell me to “stop being a b*tch” and to “grow up.” She also said she was a grown adult and could do what she wants.

I just feel hurt but maybe I’m overreacting. I don’t really have friends (social anxiety) and my mom and I were once close before she started seeing this guy.