I couldn't stand my partner's mother either, and the times we saw her I dreaded. She passed last year and none of my kids really knew her so it meant nothing, and my mother is also a narcissist so I get it. You have to set your boundaries and keep toxic people away from your family, even if they too are family. Don't invite her, the party is about your little girl. If her grandmother is going to take away from that and ruin the energy, it's not even worth it IMO
Bringing a baby into the world is a great reason to RID yourself of toxic people. Not bring them back in. Don’t invite her if she’s ruining your enjoyment. If your enjoyment at her party is depleted, so will your baby’s enjoyment be depleted. I genuinely believe our babies moods and feelings resonates with moms at least 70% of the time.