YTJ what gives you (or anyone else the right to judge someone's disability? If he said he needed the seat then that should have been the end of it. Also why are you asking on behalf of your partner? Surely she can ask for herself?
Orrrr her partner is a selfish jerk? This is what being in a relationship is all about - being there for each other not being 'repaid'. If she can't manage to be there for 2 days she's a flake to be honest
I don't think a service animal would be lying in the aisle - they are usually trained to sit under tables, chairs etc. Regardless the responsibility for this still lies with the owner - the dog shouldn't have been there (I am a dog lover!)