If she's not even able to sign into the forum she must've been writing it wrong all along unless you changed pass for the account before even trying to sign in here, then possibly done something in the process incorrectly. The username and pass is the same for forum as it is for the game.
A few things you must keep in mind when making an account and signing into the game is.
a. The password is caps lock sensitive, which means if you write a small letter where you registered with a BIG one it will come out as faulty.
b. FH doesn't get along with the numpad too well, so if you have numbers in your password you MUST use the number keys above the other letters.
c. If you registered with an extremely long username, this might not work in the game due to it's length, in that case I'd suggest to create a new account that's shorter and more simple.
The site shouldn't give faulty tokens so I must assume you are doing something wrong. Just go to this page
https://www.feral-heart.com/index.php/?option=com_user&view=resetwrite in the email linked to your sisters account, wait for it to arrive, follow the instructions inside of the mail and then log in(try to get the forum login to work first before the game OFC..). If you manage this as you should without issues and then try to log on the game without any success. Go to the site again, then login to that yellow box next to the banner and click "USER DETAILS". Inside of this you'll find 2 rows for your password. Set a new more simple password and then try to login to the game.
If this fails you should instead try to create a new account, with a new mail, and make everything as simple and short as possible to ensure it works, without numbers and just stick to letters a-z.
