Here's a thought, at her age it's possible she hurt herself in the stumble. Maybe her back. if something went in her back then you have to be careful of any carrying aids you use. They might put pressure on her back in the wrong place. I have seen several such holder upper type things and some of them would have been very bad for my dog's back.
My sister's dog was distressed, panting and off his food too though. I do believe those symptoms are not out of the norm for vestibular disease. Plus, it's been very hot where I am. Is it hot where you are? That might account for some of it too?