I followed all your steps and rechecked them. There were only two parts I wasn't sure about:
Step 4.1 I attached the whole [ACTION SetFlag("SusieHired",1)] script to the player response action bar if the player chooses to say "Let's join forces!" Was I supposed to attach the action script to the henchman's response action bar, under "Lead the way", instead?
Step 5. I have no idea what TranslatedStringKey is, but I opened the tab, clicked File, clicked New, entered NoRoom in the space, clicked Ok, added "Your party is full. There's no room for me!" under content, added "NoRoom" under Key, then saved.
The dialogue works fine but when I finish asking the character to join me he continues to stand there doing nothing.
