How often should I text this girl ? Does she likes me?

There is this girl I like and I text her once . She is rather shy and idk if she likes me . But when I ask her to exchange numbers she happily agreed and smiled . And when I talked with her , she keeps smiling .But dare not look at me . And when i was only few metres behind her , i purposely text her and i saw her take a long time to decide wat to text , wat does tis mean?When I text her she always reply and won't take more than an hour for now. When I text ttyl , she even replied bye and cya next time . Is she just being polite? Cos I only text her once she is shy but seem not shy at texting.So is it alright to text her once a day or once two days . Or few times a week ?