The sentence Shelby flittered around the room chatting with old friends and making new ones like she was a butterfly dancing on the expectant winds of spring is B. lightheaded and cheerful.
It is definitely not arrogant - there are only positive feelings in the sentence. C is also incorrect because the word childish has a negative connotation. Option D is incorrect because the sentence isn't really that meaningful.
This leaves us with B - obviously the sentence is cheerful, mentioning butterflies and fluttering wings. It is also not serious, thus lightheaded.