Personally i think if you are totally upfront that what you are selling is in fact fake i have no problem with it.

So by the same token, you don't care about theft? That is what it is, theft of Intellectual Property.

Contact Louis Vuitton and see if they will allow you to sell fake LV gear as long as the buyer knows it's fake.. I'm sure they won't agree with you and you might end up with police knocking at your door

Do I say something , or do I pretend not to care

It is up to you in the end, but you would be well within your right to report her to the police for importation of illegal goods.

She is buying the goods knowing they're fake.. Which is actually worse as she knows she is doing the wrong thing and doesn't care.

Is the Op Shop charity run? That just takes the cake if it is, not only is she supporting the importation of illegal goods, she is supporting sweat shops which is actually contradictory to what most Charities stand for..