I guess we should decide on likely CR to figure that out.  What do you think?  I'm not so good with high-powered critters.
		
		
	 
Me neither.
Well, looking through the Epic SRD monsters, she resembles the 
LeShay, who has similar two-weapon-fighting, SLAs and charm ability.
The LeShay has more HD, better ability scores and its hit points, saves  and charm DCs are a 
lot better (825 hp, Fort +29, Ref +44, Will +35, 
charm DC 53 versus the 
Hawk Lord's 277 hp, Fort +23, Ref +30, Will +24, 
charm DC 35). The LeShay's Initiative is higher, too.
The hawk lady has the flight advantage and a better AC.
I'm thinking the LeShay is better, suggesting the Hawk Lady should be a few CR lower. She's got 13 fewer HD, suggesting 3-5 CR lower. The lower stats might be worth another CR, suggesting Challenge Rating 23-26.
Of course, once we give her magical gear that might well make a CR-worthy 
difference, but currently my gut tells me she's roughly CR 24, maybe 25.
I have no idea whether she'd work that way in play, though.