Potentially various reasons, if she's getting a lot of emails, perhaps one of the few girls working in the area, then she may just read the latest ones, when she logs in and sees 100 emails and her first client is in 15 minutes then she won't have time and when he leaves the number is up to 130 she'll just ignore all previous for practicality. Perhaps your name is similar to somebody she fell out with or maybe there's something about the title, they often write don't just email saying "hi" I usually put something like "Thursday afternoon" in the title so that she'll know it's a genuine enquiry, but perhaps if she's not working on Thursday or already booked up she'll ignore it.
Also, like the rest of us, some of them are just ignorant.
