You don't get it. Their backstory and personality is way below who the character is at the top level. Their name is supergirl, a copy of superman. Their outfit is exactly the same as superman, but now with a skirt. They presumably have a similar origin story of getting their powers from being at least partially kryptonian, with nearly all the same range of powers and weaknesses.
It's lame. Making a female variation of an existing male character is weak at a fundamental level that can't be overcome. A good character is original, not a variation copy