Would there be a thoroughly investigation and even a chance to revoke her mon's PR? Yes, definitely. But there isn't any legal issue to reconcile and remarry. And there isn't any law to bar her mom to file the application. And if they can provide required evidences to satisfy the VO, then an approval is inevitable. Although I don't support this kind of behavior, but as long as it is legal, it is fine, is it?
There is no law preventing the woman from re-marrying and sponsoring her spouse but as Rob has said, IRCC would most definitely term it a "Divorce of Convenience" done specifically to circumvent the Excessive Demand rule and refuse the sponsorship app.