Do they have some kind of special wiring that can detect whether it's her grandkids calling or an angry scam victim?
Actually, they know which provider sent in the call. So they can point at the original company that allows spoofing.
Can they reach their fingers through the lines and stop the scammers from spoofing the old lady's phone number even through the call probably doesn't originate or even necessarily terminate on their lines?
I'm not sure which company regulates telecomunication laws in US, but I guess they have the authority to force it on PSTN and they *are* interested.
And the FBI. What do they have to go on? They know that someone, somewhere is spoofing her phone number. I'm not sure that is even illegal. So what basis do they have to justify the expense of an investigation?
I guess they will be interested if someone can spoof any number. Otherwise, you can call anyone passing yourself as a local FBI worker ("you can compare my caller id with your phonebook, I'm an FBI agent")
I've had my email address used by spammers as their return address.
Only clueless people will respond to a spammer - there is no defence here. But if someone blames you, you can easily prove you're right by email headers.
She should change her phone number.
Will you sponsor her new line, send notifications to all her friends&family and spend time correcting contact details in the bank, insurance company, etc.?