Hils, I would suggest you get (in advance) a stash of brochures of all sorts of things from your local tourist info office and let her browse through them in her own time when she arrives.

That will at least give you somewhere to start finding out what she would like to do, and for her to know where you are prepared to take her- she might be shy of suggesting things she would like to do.

Strolling through a large shopping centre is likely to be a good one too (unless she's already shopped out!) judging from experience with my 15 year old daughter :0)

Give me a ring if I can help.

Have a lovely time!