They gave her a flower for a prize, and she didn't want to crush it, so she didn't button up her coat.
6 seconds sound clip from the It's a Wonderful Life (1946) movie soundboard.
You can hear this line at 01:27:03 in the Blu-ray version of the movie.
Quote context
[...]
- Excuse me. Excuse me. Excuse you for what?
- All right, darling, you're excused.
- Now, go on upstairs and see if little Zuzu wants anything.
- Zuzu? What's the matter with Zuzu?
- Oh, she's just got a cold. She's in bed. Caught it coming home from school.
- What is it, a sore throat or what?
- It's just a cold. The doctor says it's nothing serious.
- The doctor? Was the doctor here?
- Yes, I called him right away. He says it's nothing to worry about.
[...]