From Ask IHG:
Can I use my points to book a reservation for someone other than myself?
Ask IHG:It is possible to use your points to book a reservation for another person. However, at this time you will need to contact us directly to book the reservation as there is no way to do this from our website.
You'd probably be OK without ringing but that would be down to the discretion of the hotel, safer to call and make sure she is added as second name on the booking.