I suppose the -a ending led to the gender-bend. I expect a male Irishman, probably with a -gh at the end. Of the name, not necessarily of the Irishman. Ahem.
In which case it'd be DARRa. Short a.
Cara would be like car with an -a. Never heard it sounding like care, and it was well used where I live at one time.
I'd pronounce
Kara the same.
I prefer the C spelling, but I find them both rather flimsy and very dated.