Oh yeah there's about a ~3.35x AP gap between Iris and Yuji, she's only got around 17.4 Tons or so
I was mainly considering her large scale attacks such as
this feat and
this feat as her main methods of approach in this fight. These attacks are very big and they do inflict a good amount of knockback so I reckon Iris could keep Yuji at bay, and Yuji doesn't have Fire Resist so I'm pretty sure he'll be pretty damaged after tanking a few of these.
Additionally, she uses Flare Magic which has relatively low base damage output, but specializes in Damage Over Time to make up for it. The more attacks she hits, the more damage Yuji's gonna take from the fire, so after a few blasts I think Yuji would be hurting severely.