Almost 90% of the countries in the world allow dual citizenship in one way or another. Like India allows OCI - that is almost Indian citizenship (without voting rights and buying agriculture lands). You can go back to your previous country any day you want in these cases. In India, you can stay lifelong with OCI, and you can even apply Indian citizenship again - if you really want that, after 7 years of living in India as OCI.
But if your wife, still doesn't want to take the oath. She needs to cancel/withdraw her citizenship application.
She is a PR and would stay with PR status as long as she satisfies it. She can renew her PR card. She will lose her PR status if she stays 1095 days (3 years) outside Canada in last 5 years (rolling date). Like in Jun 2029 - she should have stayed in Canada for more than 730 days between June 2024 - June 2029. You can only renew PR card, if you satisfy PR condition. More than 730 days in Canada in last 5 years from TODAY. TODAY is any future date, you want to apply PR card.
If in future, she wants to apply for Canadian citizenship, she should again satisfy the condition for Citizenship at that time. Her application at that time may go non-routine, as she has once withdrew her citizenship application.
From your forum chat history: it seems you are Indian in USA. I am guessing your wife is Indian too. If that is the case, Canadian passport give you visa free access to USA. You don't need to get any stamping for USA visa, ever in your life from an embassy. It solves lot of visa hassles when traveling to different countries.