Thanks all for the quick replies. Here are my takeaways ...
- Princess makes up rules that do not necessarily follow governmental requirements because they can for whatever reason, as long as they are not more lenient than government rules and in general, the 6 month rule + visas are probably the most common strict denominator (although Princess can't demand a visa if the country doesn't issue any !)
- even there is no "departure date + 6 month" rule for UK and Ireland, and England/UK will have already legitimately admitted my mom into the country when we fly in to London and embark the ship, Princess can decide to refuse her entry onto the ship if she doesn't conform to the "departure date + 6 month rule"
- although the Princess agent said to call CIBT for guidance, I can see that CIBT's interest is in getting money to do passport and visa processing, so they are probably going to quote me the same thing as Princess (departure date + 6 month rule) just to take my money, so not only will I not waste my time with CIBT, nor will I waste my time to find out if this advice was worthwhile in the first place by calling another Princess agent
- My brother had to do an expedited passport renewal last year and it caused a great deal of anxiety, but in the end, the US government did deliver on its 2-3 week commitment (phew !). Had this not been the case, I would be even less willing to go this route because she would then have NO passport available (π€they don't lose the passport during processing ! For sure i will take photos before sending it in)
- in the interest of looking at the big picture and not having a vacation ruined over $200 when we're spending way more than that for the holiday, I'll have mom go to the post office tomorrow to start the process for this reason and the reason above
Sometimes it's not worth fighting for what's right ! but better to look at the big picture. I hope this information is helpful to others. Thank you all for taking the time to give me your perspectives and guide me toward the right decision for us in this case. I appreciate your help.