My husbands ex-wife's name is on his credit card...?

When they were married he alone applied for two credit cards. They put her name on it as well but she didn't sign any papers so she likely not a co-signer. When they got divorced, he tried to get her name off the card and they said they can't do it. Apparently, she tried to with same outcome. He told her when they split, that he will take care of the dept on the card, which he is. She hasn't used it. But, now 4 years later, she received a statement and is upset that these two cards are affecting her credit rating and wants to sue. He hasn't missed any payments. How can she possibly be liable if she didn't sign any papers for her name to be put on the card initially. Because of not signing, she can't be a co-signer right? This can't be legal, right? I am missing something?? Im not sure if it makes a difference but I live in Canada. The laws might be different.