Anna only hesitates a little. She only hesitates at all because she doesn't want to seem too eager, and also... the bed is kinda small. It isn't that Elsa's too big for it, but it's a really small bed. Closer to something a child would use.
But Elsa's looking at her expectantly, and Anna can't find it in her to argue.
She does make a point of pouting and grumbling, but it's ineffective when he has to do a funny little dance because the floor is a lot colder than she was expecting.