Deleting it would make it go away completely for everyone. If you unshare it, then it will only be listed in your recipe box, but I believe it might be removed from her favorites, but if she bookmarks the recipe page, she will still be able to access it (just not likely from her recipe box). Something else she may want to consider doing is adding it as a manual entry on her nutrition tracker page and enter the nutrition info for 1 serving, then you can delete it if you want. It takes less time to do it that way and you won't need to worry about keeping it and still allowing her access to it.
Hope that helps!