Hi Tom,
Yes you can do that, and it will ask for the bitlocker key - it will be the key for her drive, so I assume it would be the key you found in her account, if her computer was set up using her account back then.
Once you have it opened with the key, it is probably best to remove the encryption. To do so, you can run Command Prompt in admin mode, run this command:
manage-bde -off D:
(Replace the drive letter with whatever it is when you connect her drive on your computer).
Give it time to finish. When it is finished, the prompt should return to the new row. Then you can run this command to verify the status:
manage-bde -status D: