It seems that last night's walk was a little too much for Louise. She already had a very active day with a couple long walks to Stanley Park and back, but while out walking with me at night, we encountered another dog that she had a slight tussle with. In the process neither dog was seriously hurt, but Louise did fall on her back. At the time, she shrugged it off and was able to continue walking with no ill effect.
By the next day, she was stiff and sore.
In fact, she has barely been outside all day and has only been out for the briefest of walks to pee a little bit. We are watching her pretty closely and hope she is a bit better by tomorrow because if this continues, we will have another vet visit. Hopefully we will see some improvement by morning.