My first thought (as a person who spent 20+ years as a vet tech in an emergency clinic) when you described symptoms was neck/back pain. Take your thumb and first finger and go down her spine, starting at just behind her head. Press in firmly on either side of her spine, moving about an inch or two between presses. Often you won't see anything except a tightening of the muscle, or a "jerk" (think of a horse or cow twitching a fly off) to indicate the pain, especially in a heavily muscled (and stoic) breed. You can also test neck pain by gently turning her head side to side, as if she was looking behind her. Movement should be smooth and easy. Dogs can have plain buffered aspirin, no more than one twice a day with food, no longer than three days in a row.