Hello everyone, I've seen lots of comments saying you liked tristana facebook page but you din't get her, and I had this same probleme. I have made lots of recherches and found out how to fix it!
You have to go on your facebook account->log in->settings->account settings->security. Then theirs gonna be ''Secure browser'', its normally enabled, you have to click ''edit'' and disable it, then you have to go on League of Legends, like it, (if you already did then skip this part), then you go on this link http://na.leagueoflegends.com/facebook and you click ''log in'', then click F5 and its gonna say something like ''You have just recieved Tristana and her Riot Girl skin'', and here you go
Me it says ''The Riot Girl skin has already been redeemed on your account.''
Hope it helped, if it did, please leave a commente