If she is currently out touring, it can be very difficult to keep up with requests.
I have an assistant who answers my new-client emails, but I handle PMs on here, P411 & a couple other sites as well.
Let me tell you: seeing a few people each day, plus travel time almost daily, replying to my repeat/regular clients who expect and deserve a personal response, posting/updating/bumping my ads, on top of the usual day-to-day that everyone has..... is very time-consuming. I do my best, but sometimes someone slips through the cracks.
When I was handling it all myself, I was constantly falling behind, which was very embarrassing for me.
Naturally I try my best not to allow this (hey, it can cost me money!!) but it does happen.
Now to address your situation: evening appointments are not MY most sought-after, but they could be for this lady. Even when I was available nearly round-the-clock, most requests were always for daytime. The most popular? Lunchtime and whatever was my earliest available.
We don't know how this lady communicates, so she may actually have you firmly scheduled and is planning to send you day-of details as the date approaches.
I strongly recommend sending a follow-up message. If you see that she has logged in to her account, and/or read your message, with no reply after a few days.... let it go.