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OP, SOGGIE'S suggestions are pretty good. If you take on duties like that, I would also suggest sending quarterly (or however often is most convenient) updates on your actions on her behalf, so she stays informed, both for her sake, and yours.
You can never have too much in writing.
I might also add, as a security measure, when sending her copies of updated documents that bear her Soc Sec Number, redact all or most the the digits. Some penal institutions have unscrupulous staff and/or inmates processing/handling inmates' mail. You can provide her with the actual un-redacted documents upon her release.
Have the inmate execute a limited power of attorney that gives you the legal right to represent them in any matter that is specifically identified in the power of attorney. A sample power of attorney would, for example, give you the right to represent them in any manner before any creditor of the inmate, any debt collector attempting to collect on a debt of the inmate, or any credit reporting agency to which credit information of the inmate has been reported.
A key question is how long she's in for. If she's in for awhile a lot of credit problems are actually going to resolve on their own. Time is the ultimate magic in building credit, and that's one thing she has in this situation. People laughed at the garden comment, but really! It's true!
I would get her report as suggested and then look through and identify which issues even need addressing. If some stuff is going to drop off her report before she's out, or shortly after--who cares? Focus on the ones that will still be around. Pay down or dispute only those accounts.
Then if you can get her set up with any kind of an account, AU on something, any kind of secured card, no matter how limited--she'll be building up credit history.
Thank you all for your responses! I will let her know to make me a power of attorney.