Should I text her or leave her be? I can't understand her?

There's a girl I met during the summer. We went home with the same public transport after summer work every day, we talked a lot. Then when summer work ended I started messaging her on Instagram sometimes, and often she texts me first. But sometimes we text a lot in the first 10-20 minutes, then she goes a bit "cold", like she doesn't respond as enthusiastically as before, or takes longer to respond, other times she's really invested in the conversation and texts a lot, not long ago she even sent me a selfie randomly. Why is this? I mean she even added me to her Close Friends list on Instagram, one time me and her both went to the cinema the same day and she wanted to meet there, asked me who I was going with to the cinema, etc. And that's after I said we should meet sometime after work (so she surely knows I like her more than a friend, at least I hope) So she clearly doesn't hate me or anything. And I'm not clingy or pushy at all because if she doesn't text me then I don't text her either. Am I boring or what?