You will need to first reinstall custom firmware on your niece's o2DS before doing anything else.
After that o2DS has
boot9strap,
Luma3DS,
GodMode9,
FBI, etc. up and running again, you will then need to find and isolate the
exact folder chain that contains your niece's library of games from that main SD card.
- sdmc:/Nintendo 3DS/<ID0>/<ID1>/
- dbs
- extdata
- title/
- 00040000 (games)
- 0004000e (updates)
- 0004008c (DLCs)
- Do not merge different <ID0> and <ID0> parent folders together.
- Do not rename the <ID0> to a different <ID0>.
- Do not move the <ID1> child folder from its real <ID0> parent folder to another <ID0> parent folder.
If you do any of these three (3) actions or variations of them, this will fuck up the original console unique
KeyY ⇄
<ID0> encryption, making it impossible to decrypt, extract, and re-encrypt the SD contents to the replacement o2DS new encryption.
***
Once you find the correct
sdmc:/Nintendo 3DS/<ID0>/<ID1> folder chain containing your niece's library of games, dlcs, updates, saves, and extdata, you're going to have to study and familiarize yourself in learning how to install and use that
ninfs program.
You will be hex viewing or image mounting the
<MMDDYY>_<serial>_sysnand_###.bin image that was backed up before the o2DS was sent to Nintendo.
- Retrieve that original (source) movable.sed.
- Mount the Nintendo 3DS folder with that (source) movable.sed.
- Copy and paste the {decrypted} dbs, extdata, and title subfolders to your computer.
- Retrieve the replacement (target) movable.sed.
- Mount the {blank newly created} Nintendo 3DS folder with that (target) movable.sed.
- Copy and paste the dbs, extdata, and title subfolders from computer to this Nintendo 3DS folder. {Re-encryption}
- Use GodMode9 to correct the CMACs, faketik to restore missing tickets, and Cthulhu to mass unwrap gift icons.
Refer to
post #2 and
post #14 for more details on how to do this.
- Do not under any circumstances restore the (source) movable.sed to the o2DS. This will fuck up access to online services like Nintendo eShop and Theme Shop. This is because that previous (source) movable.sed technically no longer belongs to your niece's replacement o2DS as far as Nintendo server records are concerned.
- If you take the "easy" route restoring the (source) movable.sed despite the above warning, just know there is a chance Nintendo may notice the discrepancy and decide to ban your o2DS from any further online services if they believe this is a case of stolen or masqueraded identity.
Here's a thread that goes in depth in why certain NAND files should not restored, shared, cloned, or transferred between different 2DS/3DS systems.
***
If your niece has user profile data (ie, Friend List, Activity Log, Notes, savedata from system titles) that are missing or not restored when signing back in and/or DSiWare games & saves, you will need to extract these constituent nand partition files from the
<MMDDYY>_<serial>_sysnand_###.bin image to the o2DS SD card.
- ctrnand_full.img
- twln.img
- twlp.img
Before making any changes to the o2DS NAND, backup the current SysNAND for extra safety. In case of a poor edit or accident, you'll want to have this to recover from.
To manually and selectively restore your niece's user setup,
- GodMode9 → press (A) on ctrnand_full.img → CTRNAND options... → Mount image to drive.
- Go in the [7:] FAT IMAGE/data/<ID0> directory. Hold (L)-shoulder and press (RIGHT) d-pad to highlight select the extdata and sysdata subfolders in yellow.
- Press (Y) to [CLIPBOARD] select these two (2) folders. If a selection mistake has occurred, press (SELECT) to reset and try again.
- Back out with (B) button. Go in the [1:] SYSNAND CTRNAND/data/<ID0> directory. Press (Y) → Copy path(s) → <A> yes → button combo → Overwrite all → <A> yes.
- Back out with (B) button. While under [root], hold (R)-shoulder and press (A) on [1:] SYSNAND CTRNAND → Fix CMACs for drive → <A> yes → button combo → <A> to continue → <A> yes.
To manually restore your niece's DSiWare games & saves,
- GodMode9 → press (A) on twln.img → Mount as FAT image → <A> yes.
- Go in the [7:] FAT IMAGE/title directory. Press (Y) on only the 00030004 folder. Do not [CLIPBOARD] select the other folders as those contain TWL system titles.
- Back out with (B) button. Go in the [2:] SYSNAND TWLN/title directory. Press (Y) → Copy path(s) → Overwrite file(s) → etc.
- Add the gm9 script CTRTransfer (Type D9) to this directory. See further instructions in how to dump, reinstall/relist the DSiWare CIAs & saves in the below post.
To manually restore your niece's photos made from
Nintendo DSi Camera (if she has any),
- GodMode9 → press (A) on twlp.img → Mount as FAT image → <A> yes.
- Press (Y) on the photo folder to add item to [CLIPBOARD].
- Back out with (B) button. Go in the [3:] SYSNAND TWLP directory. Press (Y) → Copy path(s) → Overwrite file(s) → etc.
Do not deviate from the above instructions. Follow those steps as exactly as advised. Doing something else such as copying and pasting everything within those images to the o2DS NAND partitions,
- can softbrick the 3DS firmware
- permanently erase its console unique files that should never be replaced
- risk receiving a future ban from Nintendo (ie, false identity)