Two ways:
1. She can sponsor you for PR while living in the US but then you need to prove to immigration that you will move to Canada after you get your PR. You can do this with a job offer, arranging housing beforehand, letters from friends and family stating they know your plans and will help you out or whatever else you can think of.
2. She or you both can go to Canada and she starts the sponsorship application from inside Canada. If you do an outland application, that is you officially living in the US and "visiting" her in Canada, you could expect to get your PR in give or take 6 months. You might be called for an interview in the US. Until then, if you are in Canada, you would have visitor status and would not be able to work. I would not advice to do an inland application because it takes longer and because you would be stuck in Canada and not be able to go to the US if something goes wrong in your family.
There should be a fee schedule in there somewhere. I think it's C$550 for the application fee and C$75 for the sponsorship and C$490 for the right of landing fee. Fee schedule here: http://www.cic.gc.ca/english/information/fees/fees.asp#visas_permits
