If your ATF agreed to try something that isn't usually on her menu, then consider yourself special in the first place. That she doesn't wish to try it again is completely acceptable. There was a reason it wasn't on her menu, she isn't comfortable with it. Your not being upset by it is being respectful of her boundaries. I suspect your not interested in going elsewhere not because you are whipped, but because your ATF fulfills your desires on a multitude of other levels. It's a matter of weighing the pros and cons, if she meets your desires on 9 out of 10 levels, then you are still ahead of the majority

She's your ATF because, on some level, you have some connection & she must also be good at what she does.
I suspect the service she agreed to try might be Greek.  Well, there is a whole prep cycle to doing so for many providers.  There is also a learning / training to get the muscles to relax.  A Fav of mine did not offer it for a long time but apparently read up & taught herself as it is a menu item now with proper notice.  
IMHO, this is one item outside the typical realm of providers & I'd never hold it against one who can not offer it.  
IF I really wanted Greek...  or any other service, not on her menu, then I'd quietly look elsewhere, at least when i wanted that service.
skb

I still see FBSM ladies, who have limited menus

maybe not first but in the long run. Not whipped. Just a nice respectful gentleman

When did she tell you she doesn't want to do it? If she led you to believe the two of you would continue with it if you came back again (and forked over more cash), then changed her mind when the time came, I'd say you are a little whipped. Whatever this thing is, if it crosses a boundary for her, that seems like a shoddy way to break it to you. If she told you in advance of your next date, that's different.