The driver stopped, and a small crowd gathered.
The stranger was among them, a woman who looked to be in her late 30s, she said.
She had been further up the road and had seen the accident happen, and offered to drive Mrs Luscombe and Poppy to the vet.
"I remember her saying she had animals and had been in the same situation herself," Mrs Luscombe said.
She turned down the offer and drove herself to the vet, but she found out later the woman had followed her and paid the bill after she left.
Poppy needed two operations to clean her wounds and perform skin grafts, a night in the hospital, and may still need a toe removed.
The bill added up to more than $1300, and Mrs Luscombe said paying it would have made the next few months a struggle.
When the vet called later that day to say most of the bill had been paid, she could not believe it.
"I was in shock. I sat down and burst into tears," she said.
She said she would love to meet the woman and "say a million thank yous."
"Just thinking there is a beautiful soul out there who would be kind enough to do this for me and my little dog, it shows there are still good people out there."