There are any number of anti-virus/anti-malware applications for Windows. A Google search for anti-malware windows will yield copious results including comparison tests of various products. Even Microsoft now offers their own "Safety Scanner" for Windows.
There is little worry that Windows malware can spread to Macs unless the Macs are running Windows in some environment or other. Malware on her PC could monitor and "phone home" traffic on the LAN that includes traffic to and from Macs, but that is about it.
