Making a reservation for my adult daughter. Can I book that under my Marriott number using the Marriott rewards rate even if I will not be traveling with her?
Yes, it is possible:
After making the booking call the reservations line and ask them to add her name to the booking. That way she'll be able to check in herself.
However, getting credit for the stay\points will be up to the hotel to decide (Marriott's policy doesn't allow that).
Retrieving data ...