I think going to a store where they can help you is a great idea. They can point out ones that have a lower maximum temperature.

My current one is a VS Sassoon Goddess straightener, and it's easily the best I've had. But, before this I had cheaper Remingtons and they did the job. I think for your DD this is all she'd need.

The other thing I'd advise is for her to chat to a hairdresser about looking after heat treated hair, and making sure she has the right products so that it won't end up fried if she straightens it every day.