I'll back Ousoonerfanintexas a bit on this one. Let me get this straight:
Mother comes back 1/2 hour late, imposing her lateness upon a worker who has now missed her lunch and is hungry. Hungry people get irritated. Rudeness on part of mother.
Worker continues to watch over late mother's child. Worker lashes out at mother for her lateness. Let's her know about her imposition upon her. Rudeness on part of worker.
Sounds about even to me!