I think she does need specific flaws. IMO, readers identify more with flawed characters than with perfect ones. And with specific flaws, not just the nebulous "not perfect". And real people tend to have very specific flaws, or at least things they may themselves perceive as flaws. Tony Stark is another great example, though not really what I would envision as being at all similar to Diana. I don't even care what her flaw(s) are, just that they aren't forced, seem natural, and present her with a real struggle.