Trying to answer, through this question could fit better with English.SE. My take is that, depending on how you want to see it, it is a pun or not. The video is on Youtube.
No pun intended explanation:
From the Wiktionary, a ball is also a formal dance. So it may not be a pun at all: litterally "why having a ball room if we never have guests?". This fits with the theme of the song and the beginning of the movie, since Elsa and Anna have been secluded for the most part of their life, and the coronation ball will be the first time Anna meets people since a long time.
It is actually the first time in her life she will witness a ball in the ballroom. The other lyrics are all about her excitement about the incoming party.
I am not sure that a pun was intended here, but if, by ballroom, Anna really meant a room full of balls, then it shows her innocence and naivety. This foreshadows the second part of the movie, where Anna is shown as a naive girl. Being isolated from the society for so long, her view on people are modeled on what she read and dreamed. That is not a surprise that she falls in love (or believe to be in love) with the first (falsely) charming prince she met. Parts of the lyrics of the song are about the possibility that she will meet "the one" during the party and how she idealize their first meeting.
I didn't look for words of god on the topic. Not sure it would exist anyway.