Does she already have her temporary resident visa, or are you simply hoping she will get it? In most cases, a person is awarded 6 months in Canada when they visit. Look for a hand written date on her passport when she enters. If there is no date, she gets six months by default. Otherwise, she must leave by that hand written date unless you extend her status through a direct extension or through implied status. Don't be confused by the typed date on her visa. This is the expiry of her allowed ENTRY to Canada. She must ENTER by that date. Her exit is either six months from the date of ENTRY to Canada, or the hand written date if it exists.
What others have said is correct. If you submit an extension application of some kind together with the inland application, she will have implied status until a decision is made. Put extension application in seperate envelope. Write on the envelope, "PLEASE PROCESS AFTER APPROVAL IN PRINCIPLE".
An extension application can be an application for a work permit, student permit or simply a visitors extension. Most chose work permit. Anna and I did both. We included the work permit application with her PR application. We then also applied seperately for an extension of visitor status so that she would have a physical document proving her status in Canada. With that applciation, we included proof that the inland application was about to be submitted, including proof of payment. The advantage of having explicit status rather than implied status is that without it your wife can't get a driver's licence in Canada.
