My daughter was right at 2 when she went to a twin bed, but most of my friends girls were a little older. I didn't put box springs on the bed, I put a monkey board under the mattress which keeps it low like a toddler bed. If you want to try to get her out of her crib, you should start a few months before the baby is born to get her used to it and see how she does, because that is pretty young to expect her to stay in it all night. You might consider buying one of those cribs that turns to a toddler bed, then it turns to a headboard for a twin, and if she doesn't do well, you'll have 2 cribs. Good luck!