Question about a highschool girl?

so theres this girl i like, and she's admitted that she had a huge crush on me since we were very little. and i think she still does. everytime we look at eachother, we both smile and she's been texting me lately. however, she has a boyfriend, but they've been dating for over a year, and he doesn't do anything, and she talked about how she thought she didn't think they'd be together much longer. but i was wondering if i ask her to go to the movies tomorrow, and take her to dairy queen bc she loves there quakes there. but idk how to ask her, and what are some ideas of things i can do to either tell her or show her that i care about her and i like her?? i don't want her to think im trying to break her up with her bf, but i just want to get it out to her and see what she says. thanks alot!!!