I've been an adjunct instructor at a major research university for 4 years now. So, I've seen quite a few laptops over the years. I agree you should wait until closer to the start of school. Odds are your DD doesn't know or isn't very sure what she will be majoring in yet. Many undergrads change their major the first year. So, unless she knows she'll be majoring in something that is going to require a certain machine, you're really looking for something for her to get started, do homework on, and go to class with.
Here's some things you should think about:
size: There are a couple components to this one. A bigger screen means more weight. Odds are she won't be carrying just the computer. She'll probably have at least a couple of books and a personal item (i.e. a purse and/or umbrella) also. That weight adds up. Her dorm room probably will not be right beside the building she has class in. There are parts of the campus I'm on that it can take almost 10 minutes at a brisk walk to reach.
Also important to consider about size is what kind of desks are in the classrooms. Universities usually have the following set ups: lecture halls with the VERY small fold out desks, a chair with a small fold out desk attached, a chair with an average sized table top attached, or tables. You need to consider what is at the school she'll be attending. Big screen laptops are VERY clumsy on the small desks. I've seen more than one hit the floor, and it's NEVER pretty.
Macs are not invincible. A lot of students seem to have this illusion that because they have a mac they are immune to issues. I've heard more than once from someone having computer problems. But the one thing that strikes me is when they say, "That's the funny thing, I have a Mac." Like somehow the catastrophe should have never happened to them. It's a machine, and machines break. So, it's important to always back up your work on some sort of external drive (external hard drive, USB thumb drive, etc) no matter what you decide on.
What's she used to using? Your DD is going to be making a lot of adjustments those first few weeks. Struggling with an unfamiliar OS just compounds problems. Yes, Mac and PC OS are similar, but they are also very different. Instructors usually are not very sympathetic to "I don't know how to use my computer" excuses because it gets abused so much. (That's probably the third most used excuse behind the dead grandmother who really has not passed and food poisoning. I wish students wouldn't wish ill upon their elderly relatives because it undermines people who really have had a family tragedy, and it's a horrible thing to wish on someone, but that's another story.)
I would avoid getting her one of the very small netbooks (the ones that are about as tall as a paper coffee cup). I purchased one 2 years ago when I got stuck in a classroom with a projector but no computer (I use technology a lot in my lectures). I only spent about $300 on it. I don't regret the purchase at all. It serves the purpose I got it for; however, I would NEVER want it to be my only computer. I can't imagine typing papers on it.
Finally, everyone is going to have different issues with different companies. You'll hear people that swear by Dell, Mac, HP, Toshiba, etc. Personally, I'd never buy another Toshiba again, but I know people who love theirs. I'm a Dell person, but my DH is a build-his-own person. My office mate on campus is a Mac person. Different people swear by different brands. If we all liked the same thing life would be boring.
Hope this helps.