(I'm answering based on
Disneyland...things might vary for WDW)
My guy was around that age for his first visit. Now, we went in early September, so it was just a little quieter than perhaps August might still be, and it was mid-week. And the morning started off with a huge, cold, rainstorm, so we nearly had the place to ourselves until after noon! (I highly recommend that, by the way, in Disneyland so hope for rain and bring ponchos and umbrellas

)
The "child swap" option is fabulous. Though, I would recommend to the waiting adult NOT to just sit there,waiting. I sat for AGES at Indiana Jones, just waiting with DS, when I really should have been sightseeing with him, wandering, and so on. Then my family was off the ride, and my SIL went on it with me, and it was fun.
By the time we got to POTC, DS was hungry, so he just nursed with his eyes closed throughout the ride (don't know if you're nursing a toddler, but if you are, that's a good ride to do it on!). No one was very happy with Snow White or Pinocchio, and I won't be doing those again until DS asks to see them. They are dark, with scary images, and the stories don't make sense, even if you know the story. IMO.
He loved Small World, which is good, b/c so do I. I can listen to, or sing, that song for hours at a time. As a child I nearly drove my new stepmom insane, playing the record over and over and over...

So I'm glad DS likes it, too.
DS didn't go on Buzz (I think the DL and WDW rides are different from each other?) until last year, when he was over 2, but he LOVED it. DH tells me that he doesn't think Eamon would have liked it on our first trip,though, b/c there's so much going on. A bit too overstimulating, in DH's opinion (he's the one that took DS on).
For that first trip, I wore DS on my front (facing me, b/c I never got into the forward-facing thing until I started wearing him on my back) in a mesh-paneled mei tai carrier. That was great! We did
rent a stroller, but he wasn't really comfy in it. I think the strollers are different between DL and WDW, but the ones at DL are really confining, at least for DS (he's always been tall, but never chunky).
The only line I remember was on a ride that I'm not sure is at WDW, the storybook boat ride. The line was narrow and LONG, and he did get antsy on it, but we were able to continually distract him. He was in the mei tai, and could look over my shoulder, and he interacted with the nice people around us, and with my brother and SIL (and DH of course), and the long line was dealt with in that way, with lots of distraction. It was a bit exhausting, but that was the only line I really remember!
Because we had my brother and SIL with us, we could swap people around for the child swap, which was cool. So if you have others going along, you're very lucky. If not, just ignore what I've said about my brother and SIL.
I read quite a bit in preparation, and had some good gameplans in mind. Alas, I found out that my traveling companions weren't really interested in going QUITE as fast as I wanted to, so I had to slow down, and that was fine. It still all worked out fine (especially thanks to the early rain).
Good luck! Oh, by the way, our son is really good-natured and easy-going too, and it really came through in our crazy day at D'Land. I hope your girl does the same!