Be careful with clothing... better know her size. If you get something bigger than she wears, it could be insulting. And well, if you get something smaller it could be insulting as well
Write her something. A letter, a note. Anything. Buy a blank card and tell her how much you love her and such.
A picnic is a great idea too.
If she likes manicures and facials and spas and such, get her a gift certificate.