Seems to me that if there is an FAR preventing using the bathroom, then your anger should be at the FAA and not the flight attendant or the airline.
Do you blame Col Sanders when the min wage employee screws up your order at KFC? If not, then blaming an airline for a FA is a bit excessive.
Further, blaming the FA (and calling her names???) would be excessive if she was actually following the FAA's rules.
I work for an airline.... the FAA does not care it was a little girl. The FAA does not care she wet herself. And the FAA would still punish the airline for violating the FAA's rules.
In my daily job I have to correct an instruct both customers and employees on proper methods to prevent FAA fines. Most of these issues seem stupid. The issues are things that common sense if used would if prevented the issue, but the issue will not cause a single threat to life or the flight (paperwork issues mainly). Still, we just had to pay 3,000 dollars in one single tiny paperwork issue, and each and every fine is kept on file for years. The FAA uses each and every one if those files as evidence against us whenever we have ANY issue. We have paid fines as large as 1.6M dollars and they use all these past minor fines to justify the penalty.
Long story short, the FAA has zero sense of humor and even less sense of compassion. We have been threatened with being shut down for what most people would consider a minor paperwork issue.
Lastly, if they had let the girl use the restroom and she had been injured..... Can you imagine the lawsuit?
Your beef should be with the FAA since it clearly seems the flight attendant was following company policy and the company policy was only following the FAA's rules.
Unless you can find the FAR that forbids PAX movement while the plane is taxiing and then show the section that lists bathroom emergencies as a defense against prosecution being listed -Your beef should be against the FAA.
Like I said, they have no sense of humor nor compassion.
You really should not blame the airline for not wanting to piss off (pun intended) the FAA.