To try to determine what Mrs. Higgins was thinking in "All the Years of Her Life" as she walked down the street after saving her son from being arrested from shoplifting, we first need to gather up quotes of what she did say, as that will give us some insights. She says to her son:

Be quiet, don't speak to me, you have shamed me enough, have the decency to be quiet.

And

You are a bad luck. God forgive you. It is one thing after another, always has been. Why do you stand there so stupidly? go to bed. ... Not a word about tonight to your father.

We should note that Mrs. Higgins acts very differently in different contexts. It is as we are gradually peeling away an onion to get to the core of who she is. The top layer of Mrs. Higgins is the cool, composed, polite woman who is able to talk Mr. Carr out of calling the police and impress him with her charm.

Below that layer is the mother who shows a very different face, expressing anger and disgust at her son. This layer also is concerned to keep what happened from his father, probably out of fear of her husband's reaction.

Then there is the final layer, the private self that Alfred only sees when his mother thinks nobody is looking. That self is tired and scared:

His mother's face, as she said, was a frightened, broken face. It was not the same cool, bright face he saw earlier in the drug store. As Mrs. Higgins lifted the tea cup, her hand shook. And some of the tea splashed on the table.

This final, private self is the key to writing a paragraph stating what Mrs. Higgins was thinking when she was walking down the street with her son. I can't do the assignment for you, but if you keep in mind that below her poise and anger, Mrs. Higgins is frightened and tired, what would a woman like that be saying to herself? She would probably feel at her wit's end, experiencing frustration, and be thinking about what she wished her son might do to grow up and take the pressure off of her. She would probably be thinking, too, of herself and how tired she and how old she feels. She might be wondering how long she can go on covering for him. If you think in those directions, you will probably be able to write insightfully about this character.