First, did you create the file or send a copy you had downloaded previously and what was the file suffix?
Second, it depends on whether it is a valid warning or not. What kind of PC is she using?
Third, since you used a Mac, it may have another, small, un-needed (by her OS) file attached.
Forth, it may be that some of the words un the document may have triggered the warning. If she has any control over that list it might help her to modify it.