She was AG and had a progresssive record, so she should be able to get both wings of the Democratic party aboard if she chooses a VP from the Sanders wing, like Sherrod Brown. Also, she could remind people of Obama.
Harris is pretty close to the Sanders wing...
The Sanders wing is more about personality and mostly just about whether or not you endorsed Sanders in the primary. Very little to do with ideology.
Brown isn't any farther to the left than Harris, and he definitely endorsed Clinton in the primaries(specifically, in late October 2015). I am pretty sure Harris didn't endorse anyone in the primaries.