Ok so imagine this:

High schooler Aa is anti-social. Not because Aa hates people she just can't talk to people well. Not even Aa's family, only nodding or shaking of the head, muffling sounds to answer slightly longer questions.

Bb is a social butterfly and can talk to anyone and everyone.... except Aa (lol) but Bb finds out that Aa is kind, caring, cute and loving and falls in love with Aa. Bb starts to chase Aa by different means, not by talking to Aa and professing love but in actions. Sitting by her side in the canteen, doing homework with her, inviting her to the festival etc.

Aa eventually falls in love with Bb and even though Aa still can't talk well, Aa still says this in the most clear voice Aa can give:

"I love you."