The alpaca - named Coral - had been in a private field belonging to the owners of Widmouth Farm Cottages, Ilfracombe, with her three babies.
Guests staying at the cottages watched on in horror as the dog went for Coral as she tried to protect her young last Sunday (18 April).
Owner Alison Brookes shared heartbreaking photos of the scene on Facebook, saying a man had been walking nearby with his dog off the lead.
She wrote: "So this happened about an hour ago. Our matriarch alpaca, Coral has been attacked.
"A man walking the coastal path, which borders our land, had his dog off lead. It squeezed under the gate and rounded all of our animals. Goats, sheep and alpacas.
"Coral would have stepped forward to defend the others. The man called his dog and RAN.
"This is what we are left with. She cannot stand, she has been screaming!"
She said that the vet had been to look over Coral, and that they would return again - adding that they had already lost another alpaca the year before 'for the same reason'.
"PLEASE PUT YOUR DOG ON A LEAD!" Brookes wrote.
However, Coral's owners now believe she may have to be put to sleep.
Speaking to DevonLive, Brookes' daughter Bethany explained that the vets are due to return today (22 April), but at the moment it is likely she will need to be put down.
Bethany said: "We have had three vet visits.
''It's been four days since the attack and there has been no improvements.
"We think she is paralysed from the waist down, it's so sad.
''We have tried to get her up but her back legs don't work.
''All of the other alpacas have left her now - I guess that's because in the wild they would have done that if one was injured.
''It's about what is best for her, she's in pain and discomfort. ''
Bethany said that her mother has been in contact with the police about the incident.
She added: ''What is so sad about this is that it didn't have to happen.
''Most dogs who walk along the coastal path are kept on a lead, not just for live stock but because its on a cliff edge.
''I understand accidents do happen with live stock, but I would expect an owner to come and explain the situation not run away.''
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