my sister nerver is late for school

应该改为

My sister is never late for school.

never是“频度副词”，即表示频率的,还有always,often, sometimes等等。这些副词应该放在be动词之后、其他动词之前。还例如：
He never goes to the cinema.

He is always interested in reading love stories.

my sister is never late for school.

be动词放前面

my sister is nerver late for school

be late for

my sister is never late for school

my sister is never late for school
还有 是never啦