Trojan virus

That is a phishing scam trying to get either money or information from her. Or both. Trojans and viruses on computers are two different things. It is fake, don't answer it.

Recognize and avoid phishing messages, phony support calls, and other scams - Apple Support

It's fake. Trojan horses and viruses are different types of malware; there's no such thing as a Trojan virus.

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To add, it's literally impossible for anyone to know what is on your computer via a remote message, email or web browser. Any such claim is a lie. Period. Ignore any such nonsense.