After some research, I'm highly interested in Congresswoman
Tammy Duckworth as a VP pick for Hillary if she wins the nomination. The Democrats would have to give up a potential Senate seat, but she's amazing. She's a young, Asian, female Iraq War veteran and a double amputee from combat wounds. She was born in Thailand, but her father was an American citizen, so she's a natural-born citizen.
She would be such an exciting choice.
The more I think about it, Castro would be boring. An all-female ticket would be super exciting and it'd be better for Clinton to shore up the female vote than try to appeal to men who wouldn't vote for a woman anyway. The Clinton campaign could do with some unpredictability anyway.