If she isn't traveling with you - i.e., will arive at a different time, definitely call to add her to the reservation. She will not be able to check in without you if her name isn't on the reservation.
I do agree with disney junkie, too. A few minutes on the phone now will save you time at check in. You'll be glad you called (and so will the members in line behind you, LOL)!
Best wishes -