I don't think Harris "helped" Biden, but I don't think she hurt him either.
The golden rule when picking a VP... "do not damage"
Biden had a lot of pressure to pick a women. And with the BLM protests, a black women. Anything else would have hurt him greatly.
Of all the possible VPs, Harris was the "do no damage". Biden couldn't pick a police commissioner nor a far left congresswomen.
Harris was also perfect in a way that most people know who she is.
Anyone else with lower name recognition was going to have their narrative and life been spun by Trump's campaign.