If she is your hired bookkeeper (meaning you can exert control), demand she installs an antivirus and anti-malware to your liking, even if you pay for it. Otherwise, don't let her do the work, IMO.
If this bookkeeper expects you to pay for antivirus on their system, refuse to do business. You could expose yourself to serious liability should a data breach occur and you knew that the system was not adequately protected.
I have been invited to access my own client's network to do some work and I refuse it. I want them to download to me the files that I need and then I scan it with Norton before opening the file. I am not going to risk my network.
Check with your E&O carrier first before you sign on the dotted line.