I do agree with seperating a new pet, to allow them to settle and when you are not there to watch them.

But I wouldn't use a bathroom it is uncomfortable and boring for a cat.

We always used a spare room and me & Steve took turns sleeping with the isolated cat, so they were NEVER alone at night.

We even do this with the strays we pick up (As the strays are never introduced to the family cats )

I would let the new kitten play with Blueberry when you are home and keep her in your bedroom the rest of the time.

And give it another week maybe ? to see if things settles.

PS. My kits could easily jump 4 foot. Tigs jumps from cat tree to hamg by his front paws from the window pole...I wouldn't swap them for the world.