Your mom has a lot of unspoken rage, for some reasons she's seeing you as the one who is the privileged, and everyone and everything should move around you.
She's into conspiracy theories, which could be an indication of a mental health issue going on, especially because she's extreme about it.
Possibly she's into a paranoid circle even over yourself.
From what you say I know you're truly dealing with a lot of stuff, pregnancy, work, 2 young kids, etc. nevertheless, by what you said she sees you as the entitled one, forgetting her needs, disregarding her.
That's your dynamics, right or wrong is not in question, but that's why I think she has resentment for you. And the mental health issue.
Hence her choice to not spend mothers day with you. And block you as the last resort.
You tell about abusive messages, I think that's where the key is, read through them and possibly she's telling you why she's angry .
I'd be truly upset in your shoes, really.
However sometimes people are not reasonable, having expectations of some kind, feeling neglected etc where you're actually dealing with so much yourself. And I feel there is a mental health issue too, maybe going on for all of her life, becoming manifest here.
Let the moment pass. I don't know her, you do. Kindness will help, like a card, a visit etc, but by what you said it looks like she's into a vicious circle of paranoia, phobias etc
She's dealing with a problem that you can't solve, because you're not a mental health practitioner.
Honestly without knowing her I can't say what really goes on, but certainly blocking your daughter is a sign of a disturbed relationship, where logic doesn't work.
She's your mom, you can't divorce from her, but plan how to keep a relationship with her that is safe for herself, yourself, your children.