Definitely:
MARS - fits perfectly with what you're looking for, but since it's a popular older drama you might have already seen it. I checked your list, but you've got only 2 dramas listed on there.
Maybe:
Behind Your Smile - she's a very trusting & sheltered girl. She's shy around the ml because she doesn't quite know what to make of him. He can be a bit harsh with her (he has a good reason) so that sometimes makes her shy away from him even more.
The Masked Lover - features twin sisters (played by same actress), one of whom is very shy and is a little scared of the ml at first. She is the FL & his love interest, not her more outgoing twin.
Left Ear - movie, fl is a very shy & somewhat of a wallflower. She's deaf in one ear & this makes her a bit self-conscious & shy around men in general, but esp the boy she has a crush on in high school. This isn't a pure, straightforward romance, however. It's more of a coming of age drama film.
