I was on a flight with a similar animal (yellow lab, I think) who was accompanying a blind pax. The pax had a window seat in E+, and dog sat at his feet, taking up the entire floor area of the window seat and the middle seat; the woman in the middle had a canine footrest.

I remember thinking how understanding the woman in the middle was, because I don't think I could have taken it without complaining. While I certainly wouldn't want to make the blind pax uncomfortable, and the dog was exceptionally well behaved, I would have been unhappy losing my personal space on a completely packed four-hour flight, and the truth is, I don't like dogs.