i agree that it was probably her experience at the groomer's that did it. Either they were rough with her or she had a bad run in with another dog. Albert isn't super playful but will tolerate other dogs just fine when we go to the dog park. I took him to meet my best friend's newly adopted Beagle girl over x-mas break. She was younger and bigger (not very disciplined yet) and was being excessively dominant with him..sure enough they started growling and went at each other. Luckily we each grabbed our respective dogs on time..or else they would've really let each other have it. I left immediately. He was acting very quiet and kinda bummed the rest of the night. A few days later we took him to the same dog park we always go to and he spent the entire time between our legs! When a friendly boxer tried to play with us, Al snapped on him and scared him away! It took a while for him to get back to normal! Al is a very well tempered boy!
I really hope that Thumper gets over her little hump soon..show her lots of love and definetely look into a different groomer.