If you discussed this desire BEFOR serving for the weekend no problem but, If you brought it to Me in passing after the fact and was not a part of Our agreed apon servitude structure then I would refuse on protical error and tell You possibly next time if it is brought to Me in the proper fashion. But as you can see trannie each Dominant has Their Own ways.
AS your name implies a focus on toilet service, I would not find it wrong to ask. Just don't expect more than conversation on the activity, if she has not voiced an interest in the service prior to your arrival. Sundew