The waitress
It turns out that the waitress at the restaurant was a mother herself. She was a young mother with one child and knew all about the challenges that come with raising a baby. They need a lot of support and attention and strangers can be very judgemental about the entire thing.
So when the waitress saw what was going on at Jackie’s table, she felt really sympathetic and knew she had to help in some small way. The best thing she could have done was buy one of their pizzas and show some support for a fellow mother who was trying her best.