It is outrageous you were treated so horribly! Were the 4 ladies part of Princess or were they part of a shuttle group? You never really explained that. Why did they call the sheriff over? Why did he insist you get back in the terminal. Was there some sort of security issue going on that maybe you didn't know about or were aware of? I mean he must have already been there when you went outside with you dog. You should have gotten that officer's badge number and filed a compalint against him.
Why didn't you know what was going on with the white car? I think your exhaustion played a huge part in your not understanding exactly what was going on and not being able to say "wait a minute...I'm not going anywhere until I know what is going on". It sounds like this guys was a limo driver (that's what they call hired cars in that area), probably hired by Princess to get you to your hotel room. And believe me, it seems they all drive like that, so this really isn't within Princess's control.
As far as calling these people "Princess Ground Crew", I don't think anyone involved in your mistreatment was actually employed by Princess. Princess may have hired these people in good faith to get you to a hotel, etc, since the ship had already left. Therefore, you need to notify Princess how you were abused by these people so they don't use these people anymore. Is it ultimately Princess's responsibility? Yes. And I bet if you let them know, they will not pass the buck. But, is the actual mistreatment their fault? No...these people were individual contractors and it could have happened to any cruiseline who used their services.
I hate to say it, but if you can get so fatigued that you can barely speak, barely crawl and cannot defend yourself, even verbally, against people who are abusing you, then perhaps it would be better not to travel alone. Many times in air travel or vacation travel, things happen. The best of us get exhausted and it must be brutal on someone with MS. This is one reason why most of us choose to arrive the day before and avoid the stress of possibly missing the ship. Many of us have had to learn by experience, as you just have.