Trying to convince the GF to drop Norton... I have been using the Windows defender and what ever it now called for years; never had any issues with it. If you stay away from the "free midget porn" sites you should be in good shape.
Built in Defender will find 99% of **** out there before 3rd party AV does. 3rd party AV has been more or less a scam for years. Malwarebytes has been terrible for 5+ years, but it used to be good.
Windows defender or corporate grade symantec. The paid or free home stuff is useless now that defender is around. Run a decent firewall, don't do Facebook quizzes/apps and only legit porn sites