If it were me, I would get a small gift bag and fill it with 3 or 4 little things. A fancy bar of candy, some socks, etc.
Then, get a gift card to a restaurant that they both like for the "main" gift or a gift card in general. That way ... she has a few things to "open" and then, in her birthday card, she can have a nice treat to do later.
No one complains about this sort of gift and it's fairly general, which I think is a good idea. They're not engaged, yet.
And with the smallish gifts, if she doesn't like the nice pen, book mark, small box of Godivas, little book of poetry (heck, I don't know what she likes) ... then you're not out too much money if she doesn't like the little treats.
I'll admit, though, I'm a bit of a gift giver, having like getting them myself.
Good luck,
Elisabeth
edited to add: A little gift bag of small treats is enough on it's own according to your budget. People spend more today with gifts than is my habit. So I considered a gift that would be around $50. For me, I would be more along the lines of $20-30. Again, you have to figure out a budget and keep in mind, if you go overboard with this young lady, she'll probably expect similar monetary layouts in the future.
I'm being abrupt about speaking of cash outlay. But in the end, it makes a difference. Figure out what you wish to spend, first, then go from there.
