I'm kind of surprised Iris is good for anything. She can't fight for real in her dragon form due to the permanent damage in her magic vein. Basically all she has is the dragon body, which is also incapable of flight without Matthies's help, so it's exceedingly limited in potency. Yet now she's in a human form, lacking the dragon body. Sure, she's stronger than a regular human and probably a little bit tougher, but that's it. She can't use any fancy skills involving magic because the same damaged vein is still affecting her, no matter her form. So, she's only good for beating scrubs. Ruri and Alma will probably overtake her soon enough.
But I'm kind of feeling the author is treating her situation as a matter of convenience. When it suits the plot, she's capable, when it doesn't, she's a cripple.