I Have A Chihuahua Who Is 3 Years Old. She

I have a chihuahua who is 3 years old. She has been perfectly fine up until now. Her back legs gave out and she cannot use them. I took her to the vet and she has some use of her legs she has enough use to kick the vet. The vet said its a herniated disc. They didn't even do a CT scan and said surgery would be 5,000 to 6,000. Do you have any idea what this could be from?