Well, all kids are different
But, mine was really receptive to the idea & she'd been FF for over a year when we went back to RF at about the same age as your DD.... I did a combination of things to help ease the transition:
- We bought a brand new, much comfier seat & I told her that it had to face the other direction
- I showed her pictures of other extended RF kiddos (click the 2nd line link in my signature) & we watched the crash test footage at the bottom of http://www.cpsafety.org/articles/stayrearfacing.aspx
- I had her help me uninstall the old seat & unpack the new one
- We did a living room carpet crash test fantasy role playing thing -- we acted out riding in the car, pretending kids/animals were running into the road so I "slammed the breaks", then flipped her carseat forward with her FF so that she had to use her hands to block her face from touching the floor ... when we did it all over again with her RF she giggled & realized she was safer that way
- Afterwards, she helped me install the new seat & we went shopping for some new soft carseat toys as a "reward"
We started a new routine of getting in the car, too, which just including me climbing in the back with her (because it was winter, LOL) to take off her boots & get her buckled in & cozied up with her blanky, followed by listening to her favorite music CD as soon as we got in the car for every single ride & she now had fabric books & finger puppets to play with, too.
I'm not sure which of these things made the most difference, but they all worked together well for us, LOL ... we did the same kind of fantasy role-play experiment a few months ago when she hadn't yet reached the max weight/height but wanted to turn FF in my car because she was in Grandma's & it worked again for us ... the 2nd time I encouraged her to think up various ways of positioning her feet: cross legged, dangling over the sides, straight up over the seat back, etc. & this time I took pictures to make it more playful for her (we got in another couple months RF this way before she did reach the max weight limit)