Usually if it's a problem with an old version it will tell you the PDF version is newer and things will not work. For the most part Acrobat/Reader ignores things in the PDF that it doesn't understand (ie: new functionality added in a new PDF version). If it says it's been damaged that usually means some absolutely essential section has been changed somehow. But if she emails it back to you, can you open it?
I've seen problem when emailing PDF's using some of the web based email services. Most of them have virus checking automatically done on attachments and some of those checkers actually modify the bytes slightly and that can cause problems.
While a PDF is a binary file, a lot of it is in plain text. If she opens in it in a text editor she should be able to determine if it at least looks like a PDF or if it's just complete garbage. If it's complete garbarge then something went wrong on transit. If it looks somewhat like a PDF, then I'm not sure, but try resending it and make sure no virus checker is in the way that may cause problems.
Chris
Adobe Enterprise Developer Support