Hey there, as far as I know, you have to contact CIC as soon as possible, cause as other told you, as from the moment she land and activate her PR, you will be financily responsible for her for 3 years...you need to act very fast.
Good luck
First, you need to provide a ligitimate reason for your cancelation.
Second, every story has two sides. So, we and you have to be fair before we encourage you to do so. This does not mean you have to splush all your private life in a forum like this. Just re-think..and who knows !!
Good luck