Take the 50% refund. This is an economic decision. Do not leave feedback until you have the money.
You can leave any feedback you like. Feedback is voluntary. You have 60 days to do this.
And don't feel you have to leave a positive feedback because you were only cheating of half the money you paid.
At the same time you will be asked to leave Detailed Seller Ratings. A normal rating is 5 stars. The lowest Rating is ONE STAR.
The seller admitted that her supplier isn't a good one after all.
it took a month to receive because she gets them from elswhere.
Which means she is dropshipping counterfeit items from China.
Those are ONE STAR Ratings for sure.
She can also be Reported to eBay for selling counterfeits, especially if she continues to sell the watches. If you do this, eBay will only send you a polite note. This is because while they encourage policing of listings (with over 500 000 000 listings daily, it is hard to do this themselves) they don't like to encourage vigilantes.
They will be looking into it.
You could also notify Logitech that counterfeits of their products are being sold by this seller.
You could also notify these guys:
http://www.rcmp-grc.gc.ca/pe/news-nouvelles/2010/2010-03-22-eng.htm
You can add a Response to your or her feedback at any time.
While the most efffective Responses are calm and factual, there is no need to be positive.
But apparently you left both FB and Responses before posting here. Unfortunately, this means that the seller will continue on her merry illegal scamming way.