Diana is Wonder Woman. There should be no second guessing on this statement. Whether she is dead at the moment or off earth indefinitely or in another universe, she is always Wonder Woman. For writers to slap another, like Yara, with the title is just lazy and wanting to get people to buy the mag before they realize the let down of it not being the original character.
When Artemis became Wonder Woman, I didn't think much of it because she seemed to want to be called Artemis most of the time, and of course good ole Diana was still there and we knew she would re-assume the mantle. What has Yara done to even be called Wonder Girl, as well as the douchiness of Diana giving her the 'mantle'? Absolutely nothing.
Besides, I didn't know that Diana was the one to bequeath mantles to people. Was Donna or Cassie given the title of Wonder Girl by Diana? Pretty sure no would be the answer to that question. Hence the reason why I think it was douchy of Diana to say that in the first place to Yara. It is all about DC trying to give a hard push to elevate Yara into acceptance instead of letting the masses do this by buying her comic, which they apparently didn't do or lost interest in very early on.