A Walk to Remember question

I can’t remember the name... I read a book about this teenager who killed herself and then wakes up in a different afterlife where they train her how to help prevent other people from commuting suicide as well. One of her cases was a boy and she ends up falling for him. She helps them from inside their heads and there’s a card like thing for each person and if the card is broken then the person will be lost forever and they won’t be able to help them.