first, drop the identity politics. politics is not consumer branding. people are sick and tired of this.
harris should realize that she has little experience in any substantive governing role and pick somebody older than her with a large amount of experience. the media is currently confused about the value of experience in the mind of voters. harris should not be confused with them; she should realize that an older candidate will give her legitimacy, and also that it will be a pragmatic necessity in helping her govern.
this is a list of mid-level senate seniority (the top two are republicans, chuck grassley and mitch mcconnell):
patty murray, ron wyden and dick durbin are reliable soft-left senators in safe seats. any of them would strengthen the ticket.
she wants experience and legislative know-how, not somebody that is flashy or camera friendly. her role is going to be the camera friendly one. she needs somebody competent that can actually govern.