Hi there,
It seems to me that your student doesn�t acknowledge the fact that we have to change the tense of the sentence from prent simple to past simple in reported speech.
So when we say
" Why do people come here?"
We need to report it this way:
She sked me why people came here.
Your student may ask you: " How about if we have ( Why did people come here? ) the tense of the verb is already past simple.
Well, when the verb is past simple, that will take us to the fact that we need to change the tense from past simple to past perfect, applying that:
" Why did people come here?"
We need to report it this way:
She sked me why people had come here.
She also needs to be aware that [ come ] here is past participle not present simple.
Have a nice day!