Probably the RAZR V3xx Pink. It’s girl-colored, has pretty good T9 for texting, and it’s supposed to be a great all-around phone. The only drawback is that it has a relatively short battery life. On the other hand, it’s quite thin. Note that the V3xx is different than the V3. It also comes in red. Link.
If she wants a keyboard, the Blackberry Pearl has one, and comes in red. I don’t know whether that phone is good, but it is girl-colored.