Daisy's first words are:
"I'm p-paralyzed with happiness!"
She says this to Nick, taking his hand and making him feel as if he is the only person there by the way she gazes into his eyes. This occurs in chapter 1 about 5 pages into the book.
Of course she is not literally paralyzed because she walked over to see him, but she uses the word to utter her great sense of surprise and excitement as if his presence has stunned her.
Happiness or contentment in the 20s was not just a momentary idea when a friend or relative came to town. It was a regular attitude or pursuit because entertainment was booming and fun was everywhere. So, her words could be indicative of the era, and therefore less meaningful to their personal relationship, or she could genuinely be excited beyond belief to see a beloved face from her past.
Many authors used first words to reveal something yet to come. Watch throughout the novel as you continue reading for Daisy to be stopped in her tracks by the gift of happiness. About chapters 7-8, everything changes for her.