New kitten is sitting in litter box?

Brought her home on Sunday. She hasn’t left “her room” really at all since then. She’s walked into the hallway and that’s about it. She’s just really anxious I think.

We have a resident kitten, and a dog. She has met the resident kitten, they have played and laid together and seem to be doing okay. My resident kitten just wants her to play so bad and is constantly checking on her.

When I first brought her home, she was eating the clumping litter I had, not the plain litter, but used, so I switched to silica.

Do y’all think it’s something medical? First eating her used litter and now sitting in the litter box? I’m very concerned…