A shy woman, when she likes a man, can act strangely when she is around. Especially if you've known her for a long time. For example, I may ask you strange and meaningless questions. Another behavior of a shy girl in love is to talk very fast and without making eye contact.
It can also be marked, out of the blue, in the middle of the conversation. Or she becomes restless, sighs, bends her head and seems to want to say something but can not. She really wants you to know that she likes you, but she does not know how to express her feelings without exposing herself. If you like it, invite her to spend some time together without anyone interrupting them.