Children / tweens book about a girl who travels (possibly through a portal) from a remote mountain style village to a city / town

Thhe main character is a young girl. Story begins in a remote mountain style village, but she (maybe through a portal) travels to a city / town. Not modern day. She is sort of helped by a big man who can possibly make doorways in walls. Falls in with minor criminals. Someone is trying to catch her. There is a cat with two different coloured eyes.

I know that is very vague, but I’d really appreciate any suggestions! Thanks.