In a movie I saw this sentence:
which was translated in the subs as:
She had also written letters which my grandmother received
As context, there are four characters: the writer, the speaker, the speaker's grandmother and the speaker's grand-grandmother. What happened is, the grand-grandmother hired the writer to write letters to be sent to her daughter (the speaker's grandmother), and the speaker is talking about this. So:
- Grand-grandmother: hires the writer.
- Grandmother: receives the letters
Given the context, the translation in the subs sounds right, but as far as I understand 私の祖母も彼女に手紙を書いてもらった would mean that the grandmother asked the writer to write those letters, since marked by に is the doer of the verb, and by も the one who asked to do the action.
Is there anything in the sentence indicating that's not the case? It's just the context indicating that's not the grandmother that asked to write, but rather she received the letters? I'm not sure about the grammar of this sentence, it seems at odd with what I know about a てもらう sentence (which, admittedly, still causes me some confusion).