For them stopping payment before it was posted. This is the same at any bank. Unlike a check that they present from your account, where they can stop it. There is no way to match up an electronic transaction before it posts. That is unless you knew the exact requesting company, including not only the name but their banking information. However, even then some companies get "smart" and will request payment a different way to get around any stop payments.
Most likely the dispute was denied because they probably had something that shows your mom gave them the authorization, which you even agree to. They are not going to get in the position of deciding if a company is a scam or not.
Also, just a thought for the future. If your mom is on SSI perhaps she should not be spending $600 on E-mail marketing. If she couldn't afford to "loose" what sounds like a business venture, she probably couldn't afford to spend it in the first place.