Thanks a lot Leon for clarifying this. From what I can understand from your statement, since my wife does not satisfy either of the 3 conditions you have mentioned, it would always be a risk whenever she tries to enter Canada. However, every time a person enters do they really calculate based on the PR card expiry date on whether they will be able to complete 730 days or do they not really bother as long as the PR card is valid at the moment of entry?
They may have an idea that a person does not meet the requirements. Sometimes they may give them a stern talking to. They do have the option of reporting someone for not meeting the requirements in which case they would let them enter Canada in order to prepare their appeal for their PR but if you do not meet the residency requirements and have no H&C grounds like taking care of sick relative or such, the person would most likely lose the appeal and lose their PR. However, even though they do have the option of reporting people, it does not seem to happen very often.
If your wife loses her PR, your backup option would be that you can sponsor her again.