Just be careful in how you phrase your compliment. CO is replete with beancounters, and seems to be very metrics-focused.

Saying something like, "She worked all day on my reservation," may raise eyebrows because she spent too much time on it (which is possible, but that's not the point of your letter). Being more vague and saying, "She took ownership of the problem and called me back as soon as it was resolved," gets the same point across without exposing her to any potential problems.