Is Jerry's mother a round or flat character in the story "Through the Tunnel"?

Jerry's mother is a round character because she adjusts her maternal practices and perspective of her son, allowing him to mature.

When they go to the beach on the first morning, Jerry's mother notices that he looks out at the "wild and rocky bay," and then back at the crowded beach that they have frequented for years. So, she asks her son,

"Why, darling, would you rather not come with me? Would you rather—"

But,...

Jerry's mother is a round character because she adjusts her maternal practices and perspective of her son, allowing him to mature.

When they go to the beach on the first morning, Jerry's mother notices that he looks out at the "wild and rocky bay," and then back at the crowded beach that they have frequented for years. So, she asks her son,

"Why, darling, would you rather not come with me? Would you rather—"

But, at this point, Jerry follows her. However, Jerry's mother decides to let him go to the other beach. Nevertheless, she is conflicted as she considers whether Jerry is old enough to be safe without her and how he must not feel obliged to stay with her on the beach. Her worries continue although she speaks casually to Jerry when he returns to the villa where they are staying. 

When Jerry demands swimming goggles without explanation, she gives a "patient, inquisitive look" and calmly agrees, placing her trust in her maturing boy.

When Jerry does not return until supper time, his mother still does not press Jerry about where he has been or what he has been doing; instead, she merely asks, "Did you enjoy yourself?" despite cryptic answer, "Yes."

The next day, when Jerry does not even ask permission to go to the other beach, his mother does not scold him when he returns. After he has rushed to the bathroom in order to wash the bloodstains and tear salt from his face, Jerry's mother calmly asks, "Have a nice morning?"

"Oh, yes, thank you," he said.
"You look a bit pale." And then, sharp and anxious, "How did you bang your head?"
"Oh, just banged it," he told her.
...She was worried. And then she said to herself, Oh, don't fuss. Nothing can happen. He can swim like a fish.

As they sit down to lunch together, Jerry finally opens up to his mother, telling her he can stay under water for two to three minutes. Jerry's mother then tells him that he should rest and not swim any more this day. She is ready for a battle of wills, but Jerry acquiesces at once. His mother realizes that Jerry is more mature but he is still her son, and she is satisfied that she has taken the appropriate action in allowing Jerry the freedom that she has given him.