Extension request?

Look up dual intent in the OP11 guide.
http://www.cic.gc.ca/ENGLISH/resources/manuals/op/op11-eng.pdf
Section 5.4

Edited by redeagle - 02 Jan 2010 at 5:51pm

They can flat out refuse it if they feel someone would not leave Canada at the end of their stay. I would go for 6 months. If you have a date to be married then I would sugest letting them know this, say you plan to marry in 2 months, your application goes in now then you would be married by the time the application for extension was dealt with.
Personally, I would apply common-law if possible and then update them of your marriage when it takes place.
Although it could be difficult to prove a common law relationship in somecases look at it like this; If your evidence is limited when you applied common law then you informed them that you had married, though for immigration you had no need to do so, this would probably strengthen the application as it shows you were already in the process of the application but your relationship is so genuine that you actually chose to marry for no needed reason over than love   

Like my partner was going to ask for six months from the time we expect to have an answer back on her extension?

Do you think that will be okay?

If they are going to give 6 months they probably will give it from the date they stamp it. But beware, do not get your hopes up too high, if an extension has already been given. Being refused can come as a disapointment and an immigration officer is going to ask themselves, what is the purpose of this?
Think about it, you apply for what I am thinking is a second extension, extension after extension leaves open the question of does the applicant intend to go back home after the extension is given?
The whole issue surrounding any visitor status is that the applicant will return to their home country.