How do I deposit a check made to two people when the other person is lives somewhere else?

I have a loan check made out to me and my mother since she cosigned for me. She does not live in the same place as me so I was told to have her notarize a letter authorizing me to deposit it. I did that, but the bank is still refusing to allow me to deposit it stating she has to be there physically to verify her signature. I cannot open a joint account with her b/c she is on Primary Payment. Has anyone had a similar problem? Is there anyway to deposit/cash this check?