Elsa's habit of self-imposed solitude, which had been at least on its way out back home, had come back full-force when she'd arrived in Marrowood. It made no sense for her to venture outside of her comfort zone when she wasn't entirely sure that such an action wouldn't get her killed.
When Anna had arrived, though, said solitude began to disappear again. It wasn't that Anna was forcing her out - she was just as frightened of this place as Elsa was - it was more that she wasn't comfortable with the fact that her sister could be wandering alone around the town and she'd never know. Getting out of her room some would mean that she had a better chance at keeping track of Anna.
The hotel restaurant was not her favorite place to be, but it was an intermediate step between her room and the outdoors that she found was entirely necessary.
Of course it would be the place that she ran into - or, was run into - by Hans.
She looked up at him icily, telling herself that this was good - him being near her meant that he wasn't near Anna. If she could keep herself from rash action, this could be just a minor hiccup in her day.