Is CO incentivizing collection of baggage fees at check-in? Or has anyone else has difficulty with large but legal carry-ons lately?

I have a bag that I have carried on for least 200k miles on perhaps 10 airlines (but mainly CO) all over the world. I have never been asked to check it or told it was too large before, except for RJs.

I loan it to my wife, who shows up to check in on CO 882 (BOG-IAH) on Tuesday, and she it told it is too big and that she must pay $110 to check it as a third bag. This is false, the bag is legal carry-on size.

No amount of discussion with the counter staff will change their determination to force her to pay the 110 bucks. In fact, I've carried the same d*mn bag on out of Bogota many times. The bag winds up left in Colombia.

How can this be? The bag has been carried on without incident for 200 flights or more; but suddenly, it's $110 oversize. What gives?