Follow the instruction in this form.
http://uscis.gov/graphics/formsfee/forms/i-539.htm
Once you file the application and receive the receipt notice, then you are OK to stay in US with your LP as far as her keep her status.
http://uscis.gov/graphics/formsfee/forms/i-539.htm
Once you file the application and receive the receipt notice, then you are OK to stay in US with your LP as far as her keep her status.