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I messed up by not being transparent and we have had issues with trust in the past and I know that. I should have been transparent with her but I dont know if I am just dumb for not being able to do that or if she is asking the impossible of an imperfect human?? Help.
You're not dumb; she's putting impossible standards on you while also refusing to meet any standards herself.
Talking to your best friend is not a mistake, and you shouldn't feel bad about that.
I get the sense that pwBPD
LOVE when you screw up & show remorse, because now they have a "rhetorical club" to beat you with. They can "never trust you again" now that you "betrayed" them, yadda yadda yadda... and now the ball's in your court to chase her around and reassure her, right? That's the only time she'll feel secure, because otherwise her fear of abandonment and paranoia takes over.
The fact that you're feeling guilty about looking out for yourself and your daughter is telling; I'd recommend you get help for yourself so you can start to recognize what is fair and what's not.
Looking out for yourself is fair here, and looking out for your daughter should be assumed.