One of my headcanons for lovely Iris is that although she loves Gladio very much, she has the habit of teasing her big brother and Gladio could do nothing about it
Another headcanon: Iris accidentally gave Ignis a push and before she realized (after all she was only 10) , Gladio & Ignis were together They should thank iris
Here's' the reason why I think Iris likes to tease Gladio.
P1 is the first time I played the game, Iris chose to block both Gladio & Noctis.
P2 is my second play through, she still blocked Gladio in the picture.
P3 Finally the third time, she grew a conscience.