I don't know about buying, and you also won't easily be able to restrict her in the same account where you yourself are NOT restricted.
But I wanted the same thing, for letting my parents use my iPod
And I wanted to pick which songs I considered explicit myself.
Just throw all the songs you think are explicit into a temporary playlist (just for convenience of selecting them together). Once they're there, select them ALL and add "Explicit" to the comments. Now you can delete the temp playlist and just use Smart Playlists with "Comments" Does Not Contain "Explicit."
(The way I use it: a Smart Playlist of ONLY Explicit songs. When I want to parent-proof my iPod, I just view that list, hold Command, and click a checkbox. They ALL un-check, and next time I synch my iPod, the Explicit songs are automatically gone from the library and all playlists. When I want to restore them to the iPod, I just check them back on again.)
I suggest multiple user accounts anyway--useful in many ways. You can move your iTunes Music folder to Shared--and then put the new location in iTunes Advanced Prefs. In the other user account, making the change in Prefs isn't enough--you must ALSO drag the iTunes Music folder into her iTunes window, to force it to build a song list.
Now all users can get to the music--but only you, the owner, can save changes.
And then you can set permission for CERTAIN folders/songs so that non-owners have "no access" and iTunes won't play them.
Now, how to find all the explicit songs in Finder? I'd sort the library window so they're all together. Sort by comments, probably. Then drag all the songs out of iTunes into a folder on your desktop. Change permissions (and double-check some individual files, because Finder isn't reliable for me with setting permissions) and then drag them back to iTunes. iTunes will re-import them. You'll probably end up with extra copies still on your desktop--make SURE they're extras and the delete them. Then check the ones that iTunes put in the iTunes Music folder (command-R again) and make sure they still show the custom permissions. I've never tried it to be sure whether the copies will keep that setting.
I am only 91% sure about this... and 67% sure that your song ratings and playcounts would survive the process, so back up first. And remember that you can re-build the iTunes song list by dragging the iTunes Music folder into the iTunes window at any time.
An alternative would be to keep the explicit songs NOT in your main music folder. Drag them out of iTunes into the place you want to keep them (in YOUR account, so she can't get to them), then turn OFF the pref that makes iTunes keep your music in one place. Now drag them back into iTunes. The only thing I don't know is whether they'd be copied back to Shared once you turned that pref back on. Worth a try, anyway.
