in order to build and maintain any relationship, and especially one so complex as the one in this life style, COMMUNICATION is the must. There is big difference between topping from bottom, and conveying your desire or ideas to your Master/Mistress. Subtle hints sometime work, sometime not. I dare to say it would be more likely for Mistress to pick it up than it is for Master, but in any case if there is something you have a desire for or on the other hand – you definitely do not enjoy (are disgusted by, something that ruins your experience of the scene) you should convey that to your Top. Top might oblige you and incorporate your ideas in the scene or not – that is His/Hers call and that is where the power lies. But in order for both of you to be able to experience new and exciting developments of your relationship you have to communicate.
Now, speaking from my own experience – there is nothing harder for me than to let Top know what i wish for. How are you going to reveal your desires to your Mistress is up to you. If i might suggest – maybe you should offer to read her the story, one that you particularly like (of course find one where you could put yourself into a position of a poor slave being forced to experience degradation of terrible enemas...
)
She might get the hint. Good luck!