Need to get it out....

[purgatory]

Glad to hear you worked out something that works for both of you. Stay consistent with her. If she comes over unannounced, pleasantly remind her of the need for advance notice... If she does it again, quickly make plans to leave with S and say: "I'm sorry but we already had plans, I didn't know you were coming over."

It's hard to be 'mean' to them, but just like you have to teach children the consequences of their actions, the WAS has to learn as well.

I hope this schedule works for your family, and especially your S.