L.S.
My oldest daughter was 20 months when we brought home her sister. She did great! We just had to watch her like a hawk so she didn't love her little sister TOO much - she LOVED giving her big hugs and smothering kisses :)
It's not like your daughter's going to be doing the diapering or holding the new baby unattended, right? So, just take it moment by moment. Keep reminding her that the baby is very small and we need to be very gentle. You can have her practice on a doll, but only time and practice will make her *truly* understand.