You can upgrade, but it's not like WDW; they do NOT bridge the price. I'm not sure how upgrades work if you buy a "flex" ticket that includes waterparks, etc.
First time we went we got in on some amazing deal that MapleLeafTickets had leftover, then didn't upgrade, and regretted it. Went back inside of a year and had to buy tickets all over again. That time I just bought an AP (for hotel discount...the code is APH and you can easily use that code
here to see if an AP rate shows up) and DH and DS bought tickets. By the last day, they were upgrading.
And now they have us, and have us GOOD, because the renewal rates for the APs are *so* good we kind of feel obligated to keep them going.
For discounts you need the Preferred or above. You get discounts on all sorts of merchandise and food, so always ask if there's a discount, if you get one!
Now that we've been to Universal a few times (4 visits compared to 3 WDW visits, though the Uni visits are shorter), we know that IF at all possible, we will be heading to Wizarding World if *only* to buy a Butterbeer. I get frozen, DS gets cold, and DH goes back and forth. OK, if we're a little hungry we get a Butterbeer and buy Rock Cakes from Honeydukes; they are sort of a scone-y, hard muffin-y, sort of sweet-ish treat and we LOVE them. Actually, in the morning they are terrific with a coffee from 3 Broomsticks, just to put that out there.
Anyway, if at all possible, we'll go into IOA just for that, though of course it usually turns into more than just that.
Since you don't know if you like it, you can decide if you want to walk allllll the way to the "back" of the park (and it is ALL the way back there) and all the way back, just to get a glimpse of something you haven't yet seen. It might be more magical to do it nice and refreshed, nice and EARLY in the morning.
Though if you're going to get right on Forbidden Journey or Dragon Challenge in the morning, I recommend eating *some* sort of decent breakfast before heading out. The times FJ has killed my stomach were when I was too hungry (or too full).
I'm sorry, I'm blathering on and on. Just excited for you, and it's neat that she's going right around the time that she would be getting her Hogwarts letter if she were a witch or wizard.