My 6-y.o. graddaughter is stealing and lying. I raised three kids but i never had one that stole anything especially not at the age of 6. Her parents don't know what to do either. She is very smart for her age and even seems manipulative at times. I would be greatful for any suggestions.

There is always a valid reason to what a child does.
I would seek help in understanding why she needs to do this. When the reason is understood, help is easy.
Try AuthenticParent.com for phone advice or ask at the teleclass. The girl needs kind understanding and help.
Many time stealing is a symbolic expression of feeling worthless. But there are other reasons. I cannot know what they are.