Hi Susan Could be something sinister but could be something silly as her climbing/jumping out of the car awkwardly. Or taking a corner to sharply..
A couple of days ago, one of my friend's Berners woke up like that; the night before he had been totally fine. Roached back, didn't want to eat, couldn't get in the car unaided. The vet gave him a steroid injection, some antibiotics - and the next day he ( in fact 8 hours later ) he was fine and dandy again. He still is. My friend still doesn't know what happened, but is happy that it passed so quickly. Similarly, Harvey had a "roached back & tip toeing" episode a few month ago. He screamed in agony when he jumped in the car. Again, I had no idea what brought this on. A couple of days of rest and a couple of painkillers later he was perfectly fine again. I, on the other hand, got another few grey hairs thanks to my active imagination of bone cancers, permanent disk damage and similar "nasties". Try a couple of buffered aspirins and a day or two of resting her. Chances are high that she'll be just dandy. You, meanwhile, should stock up on hair colorant! Buy lots if you plan you keep Berners. Hugs to the furries! Michaela, Harvey & Rupert Devon/UK