Usual reasons I think are one of
1. It's a Private Gallery scammer you have emailed.
2. She is an EE and did not understand what you said
3. She has it inside her AW profile text somewhere to always phone her and not to message her.
4. Your message was too long. WGs have a cut off point that they stop reading, it's something like three to four lines.
5. You asked for something she has covered in her AW profile she does not do - A-Levels, CIM etc.
6. You came across as a bit creepy in your message
7. You made a perfectly reasonable request, but one the WG did not want to personally do, so did not want to look bad rejecting it so ignored you.
8. She had read your message just before a punter was turning up for a booking and plans to reply later that evening when bookings are up
9. You asked if she would be working in a weeks time, when she does not know herself yet, so instead of replying back to say this she waits until she knows.
10. You have a red flag against your name on AW, put there by another WG, or not enough feedback as she only sees people with a certain amount of feedback.
I think those are basically the ten reasons covering all of the possible reasons why.
If you want a more specific response it of what could have been. You could post a link to the AW profile of the girl you messaged and possibly also the message you sent her.