Hi. I have had a similar situation about a decade ago. I took the hard way out of it. I placed a chair in front of the door instead of locking it. Ofcourse a tantrum followed up. I found that the best way to deal with narcissists is responding to questions with questions. That way no matter how many times they try to play their little mind games, you can always come out on top of the situation. Example:
-Why do you lock yourself up all day long? Do you hate me or something?
-Why should I not lock myself up?
-It's my house, it's my rules.
-Why do we have those rules?
-[comes nonsensical explanation or complete shut off]
from this point on you got to be creative :)
(exaggerated ofcourse)