As usual, the composition is meant for a student who is in his/her first year in school. Could someone please edit it. Thank you very much.

My mother’s name is Betty. She is thirty years old.

She eats a lot at every meal, but she does not grow fat. Her favourite food is beef.

Formerly my mother was a teacher. She is now a housewife. She stopped working because she wants to look after my younger sister and me. In the evening, she teaches me English, Chinese or mathematics. She is patient when she is teaching me. She is not teaching my young sister because she is not at school yet.

She eats a lot at every meal, but she does not grow fat. Her favourite food is beef.

Formerly, my mother was a teacher. She is now a housewife. She stopped working because she wanted to look after my younger sister and me. In the evenings, she teaches me English, Chinese or mathematics. She is patient when she is teaching me. She is not teaching my young sister because she is not in school yet.

My mother is called by the name of Betty.That's a mouthful and sounded awkward.

The original was fine. She is thirty years old.

She eats a lot at every meal, but she does not [get] grow fat. Her favourite food is beef.

Formerly, my mother was a teacher. She is now a housewife. She stopped working because she wanted to look after my younger sister and me. In the evenings, she teaches me English, Chinese or mathematics. She is patient when she is teaching me. She is not teaching my young sister because she is not in school yet.

The last sentence ' She is not teaching my younger sister because she is not in school yet. ' The part ' she is not in school ' , it means the younger sister is not in school yet. So the mother still can teach the younger sister.