So you are changing your story now?
From the OP:
Now you claim she didn't use it? And once removed from the packaging, an item like that is unsaleable.
Lets cut to the chase here. The law allows retail stores to send a letter imposing such a fine. How enforceable that law is in court is debatable. So you can take your chances on the store going to court over it.
Your daughter may have tried to mitigate her mistake by not removing the item from the store. If you want to believe she was just following along but had an attack of conscience, that's up to you. You can then deal with your punishment of her accordingly.