If you have to choose one, it may be best to go to youtube and review a walk through before you decide which one. In IOA Hogsmead has the Castle and the Forbidden Journey which you have to be 48" to ride. They also have the Flight of the Hippogryph which your daughter can ride at 36" and the Dragon Challenge looping roller coaster. The atmosphere is immersive but crowded because its smaller (or feels smaller at least). If you plan to eat there, you will still have the candy store, Three Broomsticks, the Pub and the carts to order butter bear. Also shopping if i recall was all in one place next to the wand shop and the gift shop after Forbidden Journey. Hogsmead also has a stage area for some live performances.
Diagon Alley to contrast has the London part outside and the Night Bus encounter. When you go in you have Zonkos, the Leaky Cauldron restaurant and other various different shops to look through. There is Knockturn Alley for the dark arts supplies. Of course there is Gringotts which has a height restriction of 36" and while a great experience, this is the only ride. Diagon Alley has benches to sit and have a beer outside, the Icecream shop which is the only place you can get butterbeer icecream among other flavors. It also has a bank to exchange muggle money, a stage for performances and a bit more room to spread out.
So one has more rides, great atmosphere and the castle which is a sight. The other has less rides but more shopping options some not available in Hogsmead and a bit more room to spread out. No castle but Gingotts bank is pretty cool as well. Unfortunately, you will not be able to experience the Hogwarts express or even enter to see the station as you need to present your park to park tickets to get in. Lastly if you daughter wants a wand, you will miss out on the want interactive experience in the other locations.
Hope that helps in your decision. Which is best will ultimately be up to your daughters preferences and priorities.
