No, there's no "send that old email again" option built-in.
But if you tell her to login to her account and click the My Account tab (assuming you didn't remove that link from your template), she can see all her orders history, and in every order that has downloads there will be download links. She can just click to download if it is still active.
But if the download timer has expired, you'll need to reset it within that particular order from within your Admin console. Just open that order, and click the download reset link next to the file you want to reset for her.
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