Question

she said that she is going to school改错

Answer 1

she said that she is going to school改错

正确答案是：
She said that she would going to school.

这是一个由that 引导的宾语从句。
宾语从句的结构：主句+引导词+从句。
宾语从句的三个要素/点：
1 语序：从句要用陈述语序；
2 引导词（根据句意选用不同的引导词）
3 时态：当主句是一般现在时时，从句根据句意可用不同的时态；当主句是一般过去时时，从句要用相应的过去时。

这里主句She said 是一般过去时，所以从句要用相应的过去时，即she is going to school改为 she was going to shool

Answer 2

She said she was going to school.