I have a Jack Russel Terrier, 5 years old. She was outside most of the day and in bringing her inside, she was shivering and did not want to eat and seemed lethargic all day. I have covered her up and her chills have stopped. She still seems lethargic and continues not to eat. Unsure if she has made any bowel movements today. Any suggestions? My sister is crying.

Take her to the vet. At leaste call the vet.

My first thought was paralysis tick but if she is improving it is less likely.
It could be anything from dehydration to a nervous disorder.

You need to get her to your vet as soon as possible to rule out anything nasty.