>>47500605In terms of gameplay, she's the toughest, assuming that's what you asked.
>>47500851She's the only non-player champion to canonically have beaten another champion for the spot, and Alder was specifically training himself up full-time(the training even being called ghastly) for battling her after his loss to N, so he was actually much tougher when she faced him than in BW. Her strength is also mentione in both BW1 and 2.
>>47500966If she's a native american, she's almost certainly from South America or something.
Her and Drayden's Memory Link confirms she's from a place far away from Unova.
>Drayden: Ah yes... I was thinking about the past. I traveled all over the world looking for a successor. I even went to remote places such as the Village of Dragons. That's where I met you, Iris.>Iris: Yep! I was the strongest!>Drayden: Yes. I was surprised. You were one with your Pokémon and battling with so much joy. Just watching you made me smile. Your opponents felt disappointed by their defeat, but at the same time they enjoyed the battle. It was completely natural for me to decide I wanted to make you my successor.>Iris: I'm so glad I came to Unova!