In an interview, Michael Green and Mike Johnson discuss the reboot of Kar Zor-El, and are asked about comparing her to Superman.
"The basics are similar: flight, strength, heat vision, etc. But the power levels are different, and there is a very specific reason why that will be revealed in the course of the story. And who's to say that the yellow sun affects Kryptonian males and females the same way? We will be revealing new abilities that her cousin doesn't have."
As Superman was raised by the Kents and is more comfortable with humans, that brings up an interesting point as Supergirl has had no previous human contact. Regarding Kara being so alien, they stated the following:
"We are embracing the fact that Supergirl is an alien. Maybe not as obviously as the one that Ripley blew out the airlock, but alien nonetheless. She doesn't understand human beings: how they talk, what they eat, their priorities, how they treat each other. Superman does. It's going to take time for Kara to speak English (or Italian, or Chinese, or…), time to learn how to control heat vision, time to understand why a world that can be so advanced can also be so backward."
I felt the first issue was really good, one of my favorites of week 3 of the New 52.
Head on over to IGN for more from Green and Johnson on Supergirl.