ok i've had this situation, i've had to maintain a girls interest through text for months one time, and of course the hardest part is the first few weeks, as of course, because she doesnt know you, its going to be harder.

so one thing i did unintentionally but that actually worked really well was to text her in the middle of the week, say wednesday, and directed the conversation to an interesting topic, something that gets her exited about talking to you. the topic depends on the girl, but many girls really like when you talk about them, say make readings of her personality based on stuff she says, etc. the point is that she has to want to keep the conversation going.

so i try to maintain this hook all though out the conversation, but its specially important to have her hooked before pulling this move:
what you do is text her on a wednesday night, keep the conversation going and suddenly stop responding. this should be late at night, 1) because by having her texting you late at night you have her investing in you and 2) because the next day you have the perfect excuse to keep the conversation going all day:
"heyyy im sorry i fell asleep.
(bla bla bla)"

a quick tip for daytime texting: if she is interested in you the best thing to do if you can pull this off is having a text conversation with long breaks before replying, and you will know you can pull this off if she 1) takes forever to reply too or 2) if she shows signs she is interested in the conversation (ej. makes questions) after you text her, and you have made it clear you are really occupied with your daytime activities (work, studying, etc)

hope this helps, as always if you need further advice pm me!

Jason