Well that's pretty young to have a PT, but still possible she could have a brain tumour. That would be worst case. Perhaps she's just having an off day?
There are many different behaviours that point to a neurologic problem, such as:
Poor balance, stops and stares off into space, 'forgets' they are eating, forgets how to eat (leading to weight loss), unusual chewing behaviours like chewing things up excessively, chewing on the edge of the food bowl or spoon, chewing on you, sitting more on their bum instead of haunches (usually goes with poor balance), inability to hold food normally, choosing to sleep on their own when they used to be with everyone else, squinty eyes, bruxing more than normal, bruxing harder than normal (can cause irregular wear on incisors), lack of interest in things...
These are just a few things to watch for. You know your girl the best, so if your gut tells you something is up, then listen to it.