Just read this entire thread -- where to start....?
You know your child and her habits and maturity level so if you think she's responsible enough, go for it.
Laptops are more convenient that desktops in that they can be used anywhere. My twelve-year-old has been known to watch DVD's on one on long car trips to Pennsylvania.
I just bought an Acer laptop for the house that has a full keyboard (number keys included) and a wonderful feature that has some kind of plastic cover under the keys that protects from "coke spills". Haven't actuallly tried it out yet but hopefully it'll work! I do like the color display on it -- much nicer than my Dell work laptop! Also, with our Dell laptops (Latitutde D620) , at work, we have had a fair number suffer battery failure after one year, conveniently just after the warranty expires. Replacements are quoted as $100 and that's with our major buyer negotiated price. Just an observation here for what it's worth.
This age group will set up a My space account somewhere - if not at your house, then at a friend's house. My son has one and I have his log on and password and monitor it. I only had to block a couple of friends before he passed the word that bad language won't be tolerated. I don't have a schedule for monitoring as being unpredictable is much better (the element of surprise).
Just FYI, there is a new state test on Technology Literacy that is coming down the pike within the next couple of years. Our children will need to demonstrate that they know how to operate computer application programs (right now - Word, Excel & Powerpoint). It will be a mixture of multiple choice & application questions. You might want to check with your school & see what kind of instruction they are getting in this area as it varies from county to county in the state and even from school to school. Using the programs at home offers the kids a chance to learn more about them. The pilot test will be given in 7th grade (not sure which counties are doing pilots, I know PG is one of them). This is all part of Maryland's goal for Technology Literacy by grade 8.
If you are ordering a computer online or going to Office Depot or somewhere like that, ask about the availability of a "student discount" for any software. I'm not sure if they do it for middle school but it won't hurt to ask & would save you a few dollars.
Best of luck!