If she is a Canadian citizen then she is allowed to reside abroad she would just have to include proof that she has intentions of establishing ties with Canada again as soon as it is approved. There are more threads on here to help you about that so I would look up about that on the forum. And as you know she can only visit you in the US for 6 months at a time. If the process is still not finished then and she wanted to stay longer you would need to contact others more familiar with the US visitation rule to know what she would need to do in that situation. However, I am certain she would have needed to be given a I94 stamp at the border to extend her stay. Most Canadians are not given this or even stamped when crossing the border as they are "visa-exempt".
Same goes for you if you are an American citizen then you are also "visa-exempt" to visit Canada meaning neither of you need to apply for a visitor visa before attempting to cross the border. But for more help on her side of the situation of extending her stay in the US if needed then I would recommend visiting
www.visajourney.com because they are very helpful there as well. Now, if you are asking whether when you visit about applying for an extension of your stay then we could help you there. You should also know that if she is permanent resident then she will need to continue to reside in Canada for the duration of the application and also her requirements would be a bit different to visit the US if she is a permanent resident instead so again I would ask on the forum I linked you to already. Good luck.