I am taking my 7 year old daughter for one day with park to park admission so that we can experience Wizarding World. We are at Disney for the rest of the time and will not have early entry, which is to Universal Studios the day we are going. Are we best served going to Islands of Adventure first or will it not particularly matter?
won't particularly matter. Go for the ride(s) you want. Please know if you want to do both HP sides - you need a park hopper ticket.
Diagon Alley is amazing at night, so I would suggest shooting for being there at night and do Hogsmeade first. Or just bounce back and forth.