I happily voted for Harris in the 2020 primary and I'll happily support her this time around too.
As for Rs trying to block getting her on the ballot, I don't think they have much standing. The nominating process is almost entirely controlled by the parties so as long as they decide before the cut-off dates for printing, they basically have no standing to contest it. Biden had not yet been nominated so he's not technically the candidate so there's nothing to protest there. And IIRC, the DNC bylaws require that the delegates vote for who won their state if they can do so in good conscious. If they cannot do that, they can vote how they see fit (the GOP is much more strict about who their delegates can vote for at the primary). Biden having officially dropped out opens it up for the delegates to vote basically however they would like so now I'm sure there is a lot of action going on in the background to get the party heads and delegates to come together behind Harris so that they don't have a messy convention.
To me this brings up a couple other topics...
Biden is now officially in lame duck territory. Will he start pushing for some more popular, but totally-out-there-and-not-likely-to-get-passed, big-swing legislation? Probably not because he likely doesn't want to give too much red meat to the Rs and possibly hurt Harris in the process but you never know. Maybe now's the time to try to pack the Supreme Court? I can dream, right?
Also, I like to think that this could be a huge shift in politics in general. If Harris is successful and wins in November will she be the first Gen X president (is somebody who is currently 59 Gen X? She definitely doesn't seem like a Boomer to me. This reminds me of some workplace dynamics where aging Boomers absolutely refuse to retire so we've got a big cohort of Gen X folks who are stuck in middle management, especially in the professional fields and government, that just cannot rise to those highest levels in the workplace. Beyond the question of age, what will this do for the electoral system and primary system in general? I dunno what that change may be but I could see people of whatever political persuasion being so turned off by the nominating process this cycle that this becomes a catalyst for some big change next time around. ¯\(ツ)/¯