We know Superman is pretty smart, like Reed Richards type smart. How about our Supergirl though?

Not very smart.

She was quite able in the pre-Flashpoint. But even still she wasn't known for her smarts.

In the New52 she was even less smart. She was always so impulsive and seemed to never really think things through.

In the tv show she's even worst. She wasn't even able to design and create her own suit. Not only that, if it wasn't for the DEO and her friend Winn, she wouldn't even be able to locate trouble on her own. Something Superman clearly does on his own.

Her supporting cast don't really help her shine, quite the contrary. It only serves to show how helpless she is without them.

Compared to Superman, she's always in one way or another shown to be inferior to him.

She's blonde.

Not much!

Once she promissed a kid with cancer that she would cure him. She had no idea how and went after a dude that every time he died he came back with different powers.

Her plan was to kill the guy repeatedly until he came back as a cancer healer...

Power Girl pretty blonde and she one of the smartest woman in the comic book world!