I don't think you fully understand who Susan Rice is.
She's a fairly accomplished black iwoman (Brookings Institute fellow) ...check.
She's 55 years old, so age isn't a concern....check.
She has worked closely with Biden in the past, she knows how the WH is supposed to function....check.
She was a US Ambassador, server on the NSC and National Security Advisor. There is no other woman on Biden's list who has that type of experience or could be that useful as VP....check.
She is not an activist or overly outspoken individual who wouldn't scare the moderates...check.
The only blemishes on her would be image related but are not serious - her supposed illegal meeting with Clinton on the tarmac, that's been debunked and she broke typical protocol of ex-officials about keeping their opinions about their colleagues out of the media when she called Turtle Mitch a lying piece of sh*t on one of the Pod Save episodes. And for the black militant twitter brigade, like Harris, she's married to a white man.
None of those are deal breakers. Matter of fact, those could be used to her advantage if need be.
The more I think about it, she is probably Biden's best candidate and will more than like be his pick.
EDIT: And a quick search on her - her parents were incredibly fcking accomplished, wow I didn't even know these things. She's got legit VP stock as a DC native, daughter of one of the designers of the Pell Grant and second black governor of the Federal Reserve.