Tell me this is normal and will get better?

LO has been home/or at grandmas since she was born, and just started a 2's preschool class on Monday. She is not used to getting dressed in "day" clothes, and today she refused to get "dressed", and she went to preschool in a nightgown and sweatshirt, and the moment we got to school she pulled off her pants (the high is 70 today so weather isnt too bad - but for school she really needs to wear bottoms).

Have you seen similarly dressed kids before or is this way out of the norm? Will this get better on its own or do I need to keep forcing the pants? She normally wears a dress, and at home the pants are optional... please help!