Has she really worn out a bike in three years?
Hardcore.
Carbon is only cool in the eye of the beholder. She actually asked for a new bike? You're not projecting this onto her?
If she did, go for it. Not halfway either. Get her a better bike than you've got. At least 1.5 times better. She'll be faster, more highly motivated, and more fun to ride with. Too many guys put their partners on such reject bikes and wonder why they have to wait for them.
I've advised this before.