How do you get Tristana for free?

How do you get Tristana (and the Riot Girl skin) for free? I 'liked' League of Legends on their Facebook page, then visited their redeem page, but there's nothing there to do. All it says is:

Become a fan of League of Legends on Facebook to receive the Riot Girl Tristana Skin. Click below to get yours now!

Notice: You must have visited the store in PVP.net at least once before redeeming the Riot Girl Tristana Skin.

No buttons, no fields to fill out. I am logged in on the website (my username shows up on the top bar) and Facebook.

I'm not sure what "visited the PVP.net store" means, I've bought other champions in the LoL store with IP (though not with real money), so I don't know what to do. Isn't that the "PVP.net store"? Their instructions for problems redeeming don't help either (I don't even see "the 'LoL Community Tristana' Application." on the Facebook page it links.

Solution 1:

Apparently the redemption page doesn't work properly in some browsers. I had the same issue and had to ultimately use Internet Explorer (rather than Chrome) to get Tristana.