What was annemarie scared kirsti was going to tell the soldier on the train?

Annemarie is afraid that Kristi might blow their cover and say something stupid like, "This is our friend Ellen and it's her New Year!". They had to pretend to be a family so saying that Ellen was a friend, could get them in a lot of trouble and only the Jews celebrated New Year's at that time, so it would have been too obvious that they're trying to help her escape. But she didn't. Instead, she talks about her new shoes.