hmmm (ask parent or a friend to loan u another 20)?? ice cream and a walk, coffee and a book store (if you are into that), dinner and maybe u have a cheap movie place ( i live in Oregon and we have a place where u can see movies for like 3 bucks and they are the newer and old ones. There is a bar and a food place), maybe take a drive if you drive (something scenic), well i am sure she loves to shop, go window shopping.. she would love that.. maybe mini golf, bowling, the zoo, maybe rent a movie and stuff instead of going out??? sometimes the funniest thing is just eating and talking at the mall while you people watch and talk about them (we all do it, lol don't care what anyone says. it's not judging either really it's just talking).. hmm not sure what else..
good luck and i hope you have fun with whatever u do!