The advice from my mother (3 children) and grandmother (6 children) is to wait until you have to move them out of the crib. Once they are able to climb out (and have done it), it is time to change over to a bed. Other reasons to switch: too big to sleep comfortably on small mattress, potty training (they have to be able to get to the potty), or you need the crib for the next baby. Keep in mind that she might fall out of the bed in the night, even with a safety rail.
If you don't have to, don't rush this. Enjoy each stage. It will be gone soon enough and you will wonder what happened to the time. Let your daughter progress at her own pace when you can. It will be much less stressful for both of you.
If you decide it is time, take the crib out. Don't give her a choice about sleeping in the bed. Do give her a choice between two acceptable options: would you like to sleep in your bed with this pillow or that one. The countdown idea is excellent. But however you do it, tell her what is going to happen so that she knows what to expect (and what you expect).
Make the transition a special time. Give her special privileges during the transition and tell her that's what you're doing because she's a big girl who sleeps in a bed. Read books with pictures of children sleeping in a bed. Also, when you do this, expect about a week of having to put her back in the bed many, many times. Be firm, don't talk to her, just pick her up and put her back in bed quickly, every time. If you aren't consistent or give her any attention, you can expect the transition to take longer, which will be harder on both of you.