Not that it is the CC company's fault, but isn't a co-signer there to help someone establish credit?
I'd think after 1-5 years, some validation would be done to say, co-signer is no longer needed. In other words, prompt the co-signer with a mailing and suggest they remove themself as the co-signer.
In any case, mom screwed the pooch on this one. Should've gone through her credit report and cleared that liability 10-15 years ago.
Credit cards don't work that way, there is no such thing as a "co-signer" in the traditional sense you might have with a secured loan (car, house, business, etc). If you are a named on the account then you will be responsible for the full amount of the debt, as well as have access to the entire credit line.
Additionally, if your credit sucks you will not be able to open an account with someone with good credit. The CC company most likely won't do it. Oh, they'll open the account... for the person with good credit, and make you an authorized user, but you will not be named on the account (or responsible for the debt... surprise surprise).
Many people THINK they are acting as a "co-signer" when they open an account and add someone as an authorized user who is actually the primary user... then that person stops paying the bill and the CC comes after the owner of the account, the person who is named on the account.