1) She had sent me before a point of time in the past (before you asked her to do so eg).
2) She has sent me = She did send it sometime in the past (yesterday eg but i don't know exactly when), now i say this to inform. She has already done it.
3) She sent me = She did it at a point of time in the past and we know that point . Actually this sentence should include an exact time. She sent me last month / She sent me last week ... or see it in a paragraph with the full context.