What you asking to do is very common. Make the reservation under her name. Call Marriott and have your name and Marriott Rewards number added as a second person in the room. You will receive all benefits and points, while she will still show as the primary occupant on the bill. You just need to be in the room to get the points and benefits. You don't need to be listed first.

For some reason, you can't add the second name online, or they've made it unintuitive. If you call, it will be done in seconds.