The way I see it, you are AT LEAST entitled to take advantage of any specials she runs. So don't feel bad about paying her the rate she advertises for that week. She put it out there; she intends for people to take her up on it.
Also, if you really are seeing her regularly, every week, then don't be afraid to ask her. Regulars DO get better rates with some ladies.... most ladies, I'd say. Don't expect to keep your special rate if you don't continue to be regular and reliable, though. Anyway, I'd ask, if I were you. Can't hurt, and most ladies won't throw a fit at being asked by a guy that spends a lot of time and money with them.
But to answer your question directly: No, you are not
entitled to a discount. But it would be perfectly reasonable to ask.
If she says no, just decide if you are still happy with the service for the price of her advertised rates and specials. If you are, then don't worry about a discounted rate and just have yourself a good time. If not, start shopping around.
Best of luck, love.