There are a few different office apps for Android/Kindle Fire, but frankly, they are limited in their functionality, although not bad for an Android class device. As long as there is not a big need for advanced features such as macros or advanced formatting, a Fire could do ok.
If I were making the decision, I would try to make a logical guess about whether she would use it more as a true tablet or with the keyboard. If most usage would be with the keyboard, then I think going with a laptop makes more sense.
However, for a Christmas present, I think the answer to the question could be derived more from the answer to another question... What do her friends use more and/or which do they think is cooler? :-)