From the standpoint of whether you could get on all the HP rides and at least glance at most of the shops in those areas? Yeah, probably. You'd need their equivalent of a park hopper since HP is split across both parks and you can't ride the Hogwarts Express unless your ticket is good for both.
From the standpoint of whether I think a half day in US is realistic? Probably not. Both HP areas are in the far back corners of their respective parks, so you'll be walking past aaaallll the other attractions to get in and out. While I'm less into US than Disney, I can't imagine completely ignoring every attraction outside of the Wizarding World under those circumstances. Something is going to catch her (or your) eye. If you're reasonably sure HP is all you want to do, I'd still schedule a full day so you're not going at a frantic pace and can stop and enjoy other things that might come up. If you wanted to do everything (or at least closer to "everything") I'd either go two days or go one day with ExpressPass (as I mentioned above, the cost of a two day ticket was the same as a cost of a one day ticket with ExpressPass back in 2015, so cost-wise it's six of one, half a dozen of the other).