Give her a nasty choice

You slowly grin as you realize what to do.

"OK, you have the option of fast or slow. If I go slow, you have to eat your shit and drink that piss. I will allow you all the lube you want, and make it as easy as can be for you. If you don't, however, I will fuck your ass hard and fast, and make sure to use no lube and make your ass bleed with pain."

Her face falls as she realizes you have locked the door and are standing in front of it. She has to make one of the choices.