I know this is out of date...but for any other readers...
Do something with her. I'm a step mom and have a good relationship with the step-boys.
But just hearing that she is thought of as a friend and you want to take her out for a pedi, etc is great.
Also, a family picture (try wearing shirts all the same color), and have text printed on it, Love you, or something like that.
these are just things that I would like.