This sounds fun; I love to see what kind of choices people make when they decorate.
My room WILL BE in white/navy/tan/lt green. We are still discussing paint colors for the walls, but I'm currently accessorizing in those colors.
As for your friend, I think that most people think about their bedrooms last, so she may even choose to accessorize around your gift!
If you know what colors she likes, that would be a good choice, because even if it doesn't match, she'll still love it!
Also, that is a good suggestion about checking out what she uses in other places -- I usually choose burgundys and navys for my decorating (with neutral and complimentary colors thown in, of course). Now that I'm thinking about it, my best friend uses lots of blues and tans, my mom greens and burgundys, my MIL yellows and greens and my other MIL blues and purples.
However, except for one person who has red walls, I can't think of anyone that has a non-neutral bedroom. Most of them have plain walls and the only color is in their bedding!