As a one-off, it probably isn't that bad. I'd be more concerned about the sugar, additives and fat content than the dairy aspect. Are you giving her a whole ice cream or just a small taste?
My dog *loves* sheep and goat milk products. I give her teeny tiny bits of yoghurt and cheese, and she wolfs them down. But I'm talking teaspoons, not the whole pot (much as she'd love that
Ack. I wouldn't worry about that. It's not on any forbbiden food list for dogs i.e poisonous. Funny how they like dairy, isn't it? My dog goes bananas for a soft goat cheese.