Re: Nina's experience, if she ever needs to step into the Presidency because something bad happens, you have two scenarios:
* It happens after a few years of Bernie. That means she's been a closely-involved VP for multiple years. That's plenty of experience.
* It happens early in the first term. She'll have very, very little experience...but she'll have the sympathy and good will of everybody in America who doesn't already irreversibly hate her. Expectations will be very low, she'll grow into the job, and she'll be lauded for that. The James Garfield/Chester A. Arthur scenario, basically.
As for her experience being a political liability on the ticket itself, I think we've seen that people barely care anymore. Hell, the biggest "experience" whores out there are white upper-middle-class professionals...and we've watched them go vote for Mayo in droves.