Sounds like it was simply renamed or saved with an IDML file extension. Not even close to being the same thing as exported.
Absolutely sure she used file - export - InDesignMarkup.
Then it’s possible that you have a corrupt file on your hands. Have her do it again.
But to be sure, if you’d like to send me the file I’ll be happy to take a look here.
Bob (bob AT theindesignguy DOT com)
PS to lurkers: This is not an open invitation to send me files.
Seems as if it was a corrupt file - had her save it new and re-export and it worked. Thank you!