Sandra,
I'm not sure about the situation regarding Guide dogs on QE2 - although they do have Kennels on board. You'd expect that they'd allow guide dogs - as they do on aircraft in some circumstances. I'd hope that they say 'Yes'.
Regarding smart/casual dress for dining, of the six nights transatlantic all but the first and last are 'Formal nights' - and that means dinner jacket/Tux for men and long dress for women. Smart casual is ok on the first and last nights.
Having said that - we spoke with crew on board, and when push comes to shove - they cannot INSIST that you wear formal in the dining rooms. What can they do? Clap you in irons? You would stick out like a sore thumb though if you wore denim to dinner.
The Lido is informal dining where you can wear casual clothes, but you'd be missing out if you always (and only) ate in there.
Pete