Can you cook? Maybe make dinner for them...

Or maybe rent a movie and have a movie night.

The book thing is good if you know her tastes...or maybe a gift from audible.com if she likes audiobooks (they have been such a blessing for me).

An amazon.com gift certificate is always good (that's how I got my ultrasound heat therapy machine and I love it...best birthday gift ever).

I know gift certificates don't seem very personal...but if you know they can get something they will like it might be better than trying to figure something out yourself.