Hi Rachael!
Must say, it sounds a lot like me... blessed with a very happy healthy child who puts up graciously with a loving and wanna-fix-it type Mumma. Lexi is a lucky girl.
My youngest is 8mo, and our a times are closer to 3hr-3h30. Don't get me wrong, we certainly haven't got it nailed by any means - in fact, we need help too, but just working on A times in the Average a time link, I think yours might be a bit on the short side.
I don't know for hundred percent, but that's where I'd look at for the first nap anyway. Perhaps she's just really used to 2h30 and might really resist pushing out your first a time, and you might need to stick with the first one at say 2h45 for a week, I don't know.
Someone with more know-how will post soon though!