My westie finds a pebble then sits there playing with it in her mouth, she doesn't eat it just tries to chew it and throws it up and down, does anyone elses dog do this?

I had a dog that did this. Unfortunately he chipped a tooth, which then had to be removed, ending his show career. Just keep an eye on her and make sure she doesn't swallow any. They don't come out the other end!

Harriet my Lab x BC used to do this, infact it was one of the things that attracted us to her when she was in the pen at Wood Green, she was always good at amusing herself.