J.A.
I have been told by a friend who is in the same position, that 'long' pants in kids sizes are difficult, if not impossible, to come by.
My best suggestion is learn how to sew! I am lucky and my MIL can (I am not that cool or have that much time- although I can hem a pair a pants now and then).
I would say, buy the 3T and get them on sale! If she sprouted this early, maybe she will stay that height for a little while and she will get use out of these. Just have the sides tacked in a little bit or get draw string pants...
Luckily its the summer so hopefully the shorts with elastic waistbands will be helpful for a while and maybe the rest of her will catch up!!