If she is using Norton, tell her to download the FHSetup.exe from the official download page and go into her downloads to locate the .exe. Don't have her install it, but instead, right click on it. I believe Norton has a feature that allows you to do a scan of the item and it will report back to you if it is unsafe. If she doesn't have Norton or is unwilling to do so I would be happy to provide a screenshot of the scan so she can have it as proof.
Another thing that you can tell her is that often times, anti-virus systems sometimes mark a file as harmful simply because it is by an unknown publisher, not many people have downloaded it, etc. They mark it based on statistics rather than if it really has corrupt files. I can assure you that FH is very safe, I have had it for 4+ years on multiple computers and I have not gotten a virus from it. Hope this help to clear things up. c: