I honestly don't remember if the FDM installer gives the choice of installing only for Administrator or installing for all users.
Watch for that option during the install.
...hates change and if she tries to download something and is confronted by anything other than the normal IE download window she will freak!
Your partner seems to think that IE is utter perfection.
What browser are you using?
FDM works great with Firefox.
If your not using Firefox, you might want to consider it.
Then I think you can configure FDM to work with Firefox only, leaving IE to its built-in downloader and your partner won't "see" it as an option.