If she is still married to her first husband, your marriage would be invalid under Canadian law and if that would be the case, she will likely lose her PR based on that she never should have had it.
If she had legally divorced her first husband, there is not much you can do. Your marriage would have been valid. If she left you very shortly after getting PR, you could report her, otherwise it's your word against hers that she married you only for PR. 7 years is a long time too. I am assuming she was not under condition 51 because she probably got her PR before that.
Right now, what you could do is tell immigration that you found some documents regarding your wife having been married before which she did not disclose to you and you are not certain that she had divorced her first husband and whether this means that your marriage in invalid in Canada and what effect this would have on her PR. However, it is not in your power to make immigration do anything. They would hopefully investigate and come to some conclusion.