Don't remember Mirri, does she appear after I do something?
Enslave someone then make them submit. You also need to leave your cell to have two encounters in the lower cellblock.
I got one encounter but didn't get a second encounter, do I need to do something else or just wait a bit longer?
Your slave submitted? An yeah you will probably get the second encounter at some point where you got the first one.
ah yes, my slav3 didn't summit yet
