The incident happened around 5:15pm on September 16 on an unclassified rural road to Armadale from the B8028 at Avonbridge.
The horse had to be put to sleep after the incident.
In a statement, Police Scotland said: “A 34-year-old woman has been charged in connection with a road crash, which led to the death of a horse in West Lothian.
"The incident happened around 5:15pm on Thursday, September 16 on an unclassified rural road to Armadale from the B8028 at Avonbridge.
“The horse was euthanised after the incident. No people were injured. A report will be submitted to the Procurator Fiscal in due course.”
The horse, called Solly, belonged to teenager Shona Leckie, 19, who got him four years ago.
Speaking to the Evening News last month, Ms Leckie said the animal had helped her build confidence, turning her into the rider she is today.
She said: “He was the best competition horse anyone could wish for, we won several championship titles together.
"I’ve had ponies since I was little. Mum and Dad bought Solly for me four years ago, he was the most reliable horse out there.
"He was a very successful para dressage horse with his previous owner Emma, who was paralysed from the waist down. I went to try him and felt so safe, he helped me build my confidence and I started to enjoy riding again.”
Ms Leckie added: "Solly was and always will be my horse of a lifetime. I’ll never find another like him.”