The eye contact directly affects the production of oxytocin, known as the hormone of happiness that make us feel bonded with a person. Unconsciously, we always try to make eye contact the people we like and especially with the one we have feelings for.
Thus, when your eyes meet and the girl gazes away shyly, this means that she is into you. If she is not interested, she will never do this. If you look closer and her pupils get wider when she communicates with you, this also means that she likes you.