indirect speech imperative?

A and b are both correct, but:

a. Let us say that I am hard of hearing (deaf), and someone say, " Call me when you get home." Immediately, I ask a THIRD person, " What did she say?" The third person says, " She said to call her when we GET home."

b. We are already at home, and I ask the THIRD person, " what did that lady at the party said?" Then the answer would be, " She said to call her when we GOT home."

"Call me when you get home."

The above sentence which is to be made indirect belongs to the Imperative Sentence Group.

Here the reporting clause appears omitted.So, to turn into indirect speech, a reporting clause ought to be added as you have done in answering your question.

The indirect structure will be..........

She requested/asked/advised (us) to call her when we GOT home.

Your alternative"b" is correct as the reporting verb in the direct speech is in the Past Tense.

Thanks.

Direct: She said, "Call me when you get home."

Indirect: She said to call her when we get home.

"She said to call her when we get home" means that when you get home, she wants you to call her.

"She said to call her when we got home" means that when you got home she said "call me". She said it when you got home.

the word should be "got"... the sentence it is subordinate to is in the past "she said...", so the verb in should also be in the past...

In the first sentence, everything is in the present, so "get" is OK

got is correct