What expression she's trying to make?

When a girl is shy and reserved and doesn't have many friend, has nerdy hobbies and most of her social life comes from a MMO, then in her last year of high school there's a boy in her class who she thinks is pretty cute, he's not the most popular guy but he has a good circle of friend and is always making people laugh and she starts liking him from afar and think she'll never be with him, then one day she gets grouped together with him and three other students for a school project where they have to create a mini-movie, their group make plans on when and where to meet up to do this and the boy she likes has a big backyard so they decide to film at his place during the weekend, after doing the filming it's late so they make plans to meet up next weekend for the editing part, the other students' parents comes to pick them up but her father called and said someone hit his car and it's nothing big but he has to deal with the police and he can't come pick her up, her aunt can go pick her up but she's working the weekend shift so only after 8pm, so the boy's parent say she can stay for dinner, after dinner the boy says might as well get ready for next week so they go on his computer to download a movie editing software, she sees on the desktop the icon for the MMO she plays and mentions it, it turns out they both play on the same server and he's surprised a girl near him plays it, during the following weeks they start playing together and speaking to each other more at school, at the end of the year he invites her to prom and she's surprised and super happy, then on the day of the prom he goes to pick her up and knock on the door, she answers and says "Sorry, I just need to finish getting dressed, give me 5 minutes!", then he teases her and say he wouldn't mind watching her get dressed and even tough she's being teased she also likes the attention, at that precise moment she makes that exact expression.