Yep, sellers can no longer leave negative feedback for buyers.

I think if you have had a negative experience (which it sounds like you have - no item, lack of communication or refund) then you should leave negative feedback. I seriously doubt she will refund you now if she hasn't already. How long does a PayPal dispute take to resolve? Is it worth waiting until it is resolved until you leave feedback? Make sure you can still leave feedback too, I think there is only a certain amount of days available that you can actually leave feedback, after that you can't leave any.

Good luck