I think there are some other issues to think about.
1) Can she open doors
2) Does she get into things
3) Do you think if she woke up early, she would get into things while everyone is asleep (we had a ketchup incident with our oldest)
I do think that making the transition early could be easier. Sometimes it's best to prevent the problem instead of waiting until you have to deal with it. I can imagine that if your little girl is obedient and listens to you well, you could switch her now and get into a good routine before she gets too opinionated and terrible-twoish. Right now, my 2 year old is opinionated, doesn't listen, and fights bed and nap-times. Now is not a good time for us to address a new bed for him! Besides, today, even while Daddy was home with him, he got into the fridge and ate 4 cartons of yogurt before I came home and caught him. That would happen every morning if he weren't in a crib!
I also agree that you could ask your daughter. When I converted oldest son's crib into a toddler bed, he woke up every night screaming by his door. I put the side back on and we all slept well for a few more months. Then we put a guest bed in his bedroom, and I saw him eying it. I asked him if he wanted to sleep in the big bed, he nodded, and that was it! it's amazing how willing they are to be obey new rules (for sleeping in a big bed, like if you wake up and it's dark, go back to sleep. if it's light, come wake up mommy) when it's their idea.
Oh, and one more thing that I hadn't thought of, but someone mentioned it. Potty Training! yeah, they really need to be able to get up in the middle of the night to go potty on their own, so you'll need to get her out of a crib before you start that. Dang, I guess that means I need to get my 25 month old out sooner than i thought!
Good luck!