One of the men later came forward to say he had no idea she was disabled, and that the train company had announced all reservations were cancelled.
Hoyle said she saw the three women leave the dog's mess on the ground at Padstow in north Cornwall on Thursday, while on their way to the ferry to nearby Rock.
She wrote in a public message to the council on Facebook: "There [sic] blonde Great Dane did his business on the neat and tidy cut grass that was packed with tourists and then they all walked off leaving the mess behind. I would not report this if it was a small dog but this was a Great Dane!! And the mess left was enormous."
Hoyle went on to say she had taken a photograph of the mess next to a pen to show the scale. She said: "These ladies were offered a poo bag by myself on the beach and they said they had one.
"I suggested politely in that case they should return and pick up the mess as they had time before the ferry left.
"They refused to do so. They were further challenged by a gentleman and still refused to pick the mess up."
Hoyle, 44, claims the women, who were walking two Great Danes and an Alsatian, had asked her: "Who are you to tell us?" But she added in her post: "I am a responsible dog owner who lives in the area regularly walking my dog."
Hoyle's Facebook post was shared nearly 5,000 times and attracted more than 1,000 comments. One user wrote: "Disgusting. If you won't pick up dog mess don't own a dog, simple."
Hoyle edited the message on Thursday evening, saying: "Update: woman has now come forward - let's leave council to now deal with".
The owner of the offending dog, who asked not to be named, expressed regret for her actions to a local newspaper. "My friend had the dog and I was on the beach waiting for the ferry when it made the mess in the rough grass area," she said.
"I was the one who had the bags. In hindsight, although I was not walking the dog at the time, I became aware and I should have gone back up and cleaned up the mess, missed the ferry and taken the next one."
A Cornwall Council spokesman said: "There has been a huge public reaction to the Facebook post from a concerned resident reporting alleged dog fouling. The dog owner has since come forward and we are dealing with the incident.
"The issue of dog fouling is one that upsets and angers many residents and we encourage members of the public to report incidents to us.
"The message to irresponsible dog owners is that if you don't clear up after your dog, we will do all that we can to track you down and issue you with a fixed penalty notice."
Fines for refusing to clean up after your dog vary across the UK, but are often around £50 (NZ$90) and can be as much as £80 (NZ$143). Those who do not pay can be taken to court and fined up to £1,000 (NZ$1,790).
Some local authorities make it mandatory for owners to carry a "poop scoop" and disposable bag when they are walking their dog in a public place.
