:( That's a bummer. I'm sorry.
Honestly, I think you're right that this is no loss, and the "how dare you share cake with her" thing is bizarre. It sounds like this friendship pretty mutually tapered off a while ago- like you said, it happens.
I will say that some of the people I know that have problematic/ bizarre/ explosive behaviors also tend to see a lot of causality where there might not be any- as in, instead of being able to say, "Yeah, we kind of grew apart, lives went in different directions, you know," for them it's, "They used to be in my life but aren't anymore, therefore they must hate me/ judge me/ have something against me. How dare they! Now I don't like them either." So I wanted to throw that out there- she might not be at a place emotionally where she can process that someone who isn't part of her life has nothing against her.