Hello, My Friend And I Are Having A Dispute Regarding

Hello,
My friend and I are having a dispute regarding the pathology of hepatitis C. She has been told that it is possible to acquire the virus not by sharing needles, but by re-using one's own disposable syringes, when the fluid path is contaminated with traces of aged blood. Ostensibly, I suppose that the virus is supposed to incubate following the first use of a syringe, and then becomes auto-infectious when used again.
However, I don't think that's quite how it works. I'm under the impression that the hep C virus requires transmission specifically from an infected person, such as an instance of sharing needles with an individual already suffering from it. However, I believe that there are other types of hepatitis, and situations in which it is a symptom, from various bacterial and viral enviromental pathogens that can be easily cultured in old blood, which lends her theory some credence. Is this correct, or can hepatitis C simply manifest as my friend says?