Thank you for taking the time to look this up. With the great info from yourself & @ura-soul I have been reading up on this for the last hour and feel sure what we are looking at here is partial oculomotor palsy. And (as I mentioned to @ura-soul) "There is some evidence of a familial tendency to the condition" which made me think of some minor abnormalities I have spotted with one of Sabrina's eyes.

I will be giving her a quick eye test when she wakes up. Something similar to the bird on the pen test!

I feel certain this is genetic now. Though I will know more in an hour ;)