Most Helpful Girl
You can text first as long as it's relevant and not too often. Maybe sometimes wait for her to say something instead... and never send a second message without a reply to the previous one1
Most Helpful Guy
I have been in this exact situation bro.
Best thing to do is ask. Just start a convo and any time you want just ask ' why don't you message me first (just curious)?' Or something along those lines bro then you'll get and answer
When I asked this the girl just said 'I don't want to bother you or annoy you' :)1