Recovering Files From Hard Drive

Hi there. Recently, my friend's mid 2012 MacBook Pro appeared to die in a slightly odd way. She got the "circle-with a line through it" symbol, which google attributed to not detecting the hard drive. I found that if you booted up the computer, it would get fair enough to select either her user account or a guest. If you boot up as a guest, with only access to safari, it boots successfully. If you boot into her user account, it loads for a bit and then fails, displaying the same original error symbol.

I've now replaced her hard drive and her computer is running just fine, however we'd like to retrieve her files from the old drive, if possible. I've got an external USB SATA connector for using any 2.5 inch drive as an external hard drive. When I connect the hard drive over USB, it quickly asks for a password to unlock the disk:

I should note, when entering the password, it often takes multiple tries with the correct password for it to accept it. Once it does, it gives you this message:

If you comply, and select "Launch Disk Utility", you just get an endless loading screen:

If you plug in the drive, ignore the password popup or outright hit "cancel", and go to disk utility, your options are pretty limited:

The drive doesn't even show up in finder. Here's some terminal for you as well:

#: TYPE NAME SIZE IDENTIFIER

0: GUID_partition_scheme *500.1 GB disk3

1: EFI EFI 209.7 MB disk3s1

2: Apple_CoreStorage Macintosh HD 499.2 GB disk3s2

3: Apple_Boot Boot OS X 650.0 MB disk3s3

Offline

Logical Volume Macintosh HD on disk3s2

F1E6782A-64B4-4C18-8E0C-63287E488918

Locked Encrypted

ChristophersAir:~ user$

(Note that it says the volume is in fact encrypted)

ChristophersAir:~ user$ diskutil mount disk3s2

disk3s2 is a FileVault or Fusion Drive physical volume; use "diskutil coreStorage list" to find its logical volume, which you can then unlock (if necessary) and mount

ChristophersAir:~ user$ diskutil coreStorage list

CoreStorage logical volume groups (1 found)

|

+-- Logical Volume Group 640715C4-00D9-41F3-B871-126C72CEF477

=========================================================

Name: Macintosh HD

Status: Online

Size: 499248103424 B (499.2 GB)

Free Space: 18972672 B (19.0 MB)

|

+-< Physical Volume 24C55300-95C3-4B2E-A654-8BC28F8159E6

| ----------------------------------------------------

| Index: 0

| Disk: disk3s2

| Status: Online

| Size: 499248103424 B (499.2 GB)

|

+-> Logical Volume Family D300FC15-82CC-458D-8455-4582FAA97AE5

----------------------------------------------------------

Encryption Type: AES-XTS

Encryption Status: Locked

Conversion Status: Complete

High Level Queries: Fully Secure

| Passphrase Required

| Accepts New Users

| Has Visible Users

| Has Volume Key

|

+-> Logical Volume F1E6782A-64B4-4C18-8E0C-63287E488918

---------------------------------------------------

Disk: -none-

Status: Locked

Size (Total): 498876809216 B (498.9 GB)

Revertible: Yes (unlock and decryption required)

LV Name: Macintosh HD

Content Hint: Apple_HFS

ChristophersAir:~user$ diskutil coreStorage unlockVolume F1E6782A-64B4-4C18-8E0C-63287E488918

Passphrase:

Started CoreStorage operation

Error: -69749: Unable to unlock the Core Storage volume

I'm at a loss for where to go next, I'm afraid. Any help would be very much appreciated.