From USA to Canada?

No, this is not possible.

If your friend is here on a B-2 (tourist) visa and wishes to stay beyond the time indicated on their Form I-94 then they must contact the Department of Homeland Security’s Bureau of Citizenship and Immigration Services to request an application to extend status.

The decision to grant or deny a request for extension of stay is made solely by the Bureau of Citizenship and Immigration Services.

To learn more about the procedures to extend your stay then visit the website I have provided below.

*Note however, that if she extends her stay, then it is still not possible for her to work in the United States.

Edit:

Nrb660 - I think you are missing the point of the question entirely. The person in question stated that her friends TOURIST (B-2) visa as nearly expired and wondered if it were possible to travel to Canada, stay for a while and then drive back an be able to obtain another 3-month tourist visa rather than flying home to do so.

and the answer is, no she can't. You can only apply for a new tourist visa at the embassy in your home country. If you want it renewed then I have provided the link with the details explaining how.

There was no mention of a work permit and since the person in question is here on a tourist visa then they legally can't seek or gain employment of any kind.

YES she can, provided she has the work permit approved.

Alot of Canadians work in the US & commute daily.