Is it okay to lock a kitten in a dark, windowless closet every time she is alone?

by RBell
(Mesa, AZ, USA)

My friend brought home her new kitten who is adopted and a few weeks old. She already has three dogs, one big, one medium, and one small.

The large older dog could care less and is not afraid of the kitten. Initially the medium and small sized dogs nipped her when they first met.

Now, the medium dog is warming up and likes her, but the small dog is terrified of her. In fact, the small dog runs away, hides and pees (sometimes) when I walk by with the kitten in my arms.

Since I do not live there, I have never seen the small dog's interaction with the kitten and therefore never scolded the dog for its behavior.

It is my understanding that the small dog has a negative history with stray cats in the area. When he was found on the street, he had clearly been abused by someone and most likely was attacked by the cats as well.

Because of all this, my friend puts the kitten in a dark windowless closet with the door closed whenever no one is home and at night. When we bring the kitten out, it purrs like a motor boat and is super playful and loving.

When we go to bring her back to the room with the closet "prison," she cries and tries her hardest to get away from us just to stay out of that room.

The litter box, food and water are in the closet but something just seems wrong about it. The kitten knows the small dog that doesn't like her is outside the closet door and ultimately just seems terrified of that room.

I have read up on how to properly introduce new pets, but what do you do when the dog has PTSD towards cats in general, and is it okay to lock up a kitten in that way?