A CDR may or may not have accurate information as to the source of the call. If the call is entirely local (the LEC handles call termination on both ends as well as transit), then it should have all the information. However, if the call transits a different carrier, then the LEC that handles termination for the target of the scammer only knows the caller ID that was passed to it from the transit carrier. If it's unknown, then that's what is passed into the CDR. You may be able to glean other source information about the handoff to the transit carrier, then get THEM involved to find the call that was routed to that handoff at that time, and so on.

Oh, and since those aren't her calls (the scammer wasn't calling HER), then you must have a subpoena. If one of the scam targets cooperates, then THEY might be able to request their own records, but to get intervening carriers to cooperate, you'll need a lawyer or law enforcement. I'd try the latter, first. Keywords like "terroristic threats" and such may get you some attention. Once you know it crosses state lines, and perhaps some idea of how wide sweeping the scope is, then you might have something the FBI can/will look at. Try your local state bureau of investigation first, as they may have more immediate resources.

Ob. disclaimer: Though employed in telecom, I am not a lawyer.