Go to this page where the forms are: http://www.cic.gc.ca/english/information/applications/visitor.asp and scroll down. It will offer you the option to apply online or to send the application to Vegreville. It gives the address.
When you get the receipt, you can take it to a bank and pay it there. They will stamp it and you send it with the application.
Note for the future that you should always apply to extend a visa 30 days before it expires. However, as long as you do it before it expires, it's not a big deal with the 30 days. After it expires, there is a 90 day grace period to either restore status or leave.
Once you have applied, you have implied status. That means she is allowed to stay while you wait for immigration to process the application even though she may have passed the 90 day grace period by then.