I find it silly when people say "oh just shut up Hillary, you lost go away." Gore lost, then became a major climate change activist. Kerry lost, nine years later became Secretary of State. McCain lost, stayed in the Senate and has been an important figure in the Senate quite often. Only Romney has really disappeared, and even then I don't recall people complaining "romney should just shut up and go away." I mean Clinton won the popular vote by a larger margin than Kennedy in '60, Nixon in '68, Carter in '76, and Gore in '00; she's not so unpopular as to have people shut her up and dismiss her. I wouldn't support her in 2020, but I still like her and I'm sure she'll have fun running her new PAC.
What's working against Hillary is that she lost two high profile races where she was the favorite going in. She has baggage and isn't a great candidate/campaigner (even if many think she'd be a strong president, she has to get elected first and she's twice proven she can't win on a national stage). And she didn't lose to a sane respectable Republican like McCain. She lost to an incompetent, scandal plagued, hot mess of a candidate. That's just embarrassing. Since Trump is such a train wreck, I don't see many people risking 4 more years of the man child by jumping on the Hillary bandwagon that has epically gone up in flames twice before. Like Gore, it'd be best for Hillary to find an issue she cares about and dedicate her time to that. Since she's done a lot of work with children's issues, that seems like a natural fit. Maybe dealing with childhood poverty and advocating for paid family leave? The party needs to thank the Clintons for their service and move on. She'd just be doing the party a huge disservice by throwing her name in the ring again.