Possibly. It's inconclusive. However Kara doesn't have anywhere near the experience to take on Diana. Someday but not now. She had trouble with Clayface for goodness's sake.
That bull**** story. Clayface somehow managed to steal her "magic" clay. Which is bull**** because Diana is completely human. She hasn't been clay since she was on the beaches of Themyscira.
I'm still inclined to go with Supergirl, if she's strong enough to give superman serious trouble I think she could beat WW. The heat vision would come in real handy in this battle.
.....hmmm.... probably because Superman knows how to hold back better than her
Superman is always underselling himself like that....... i bet he could take out half the guys he claims are threats fairly eaily if he didn't hold back so much
supergirl didnt have problems with clay face, you all know you can lie. she was knocked out of a building during a fight with batgirl and clay face was standing over her. she picked up the ground beneath him and she flew him in the ocean, it was as simple as that. It did state in that book that she is more powerful than superman. Superman was suprised when they were flying in space, testing there speed and she disappeared, she left him at the moon while she was already back on earth. They also said in that book that she is stronger than him, when she was holding a crashing plane with 1 hand. I think supergirl wins this due to the fact that she is everything wonderwomen is but fighting skills.
Supergirl can match(even surpass) her in raw power, but she lacks experience. Mebbe in like, a decade or so she could give Diana a run for her money but not now.
As for the "Supergirl is stronger than Superman" thing:
It's because Superman was raised by humans, so he sees himself as a human (more or less) ie he has limits. "I can't lift <insert object>" "I can't see that far"and whatnot.
Supergirl was raised as a Kryptonian, and she doesn't see herself as human, so she's not like "I can't fly that fast"--she just does it.
Their strength and flight are due to telekinesis, so I'm guessing if they don't believe they can lift something then they can't, and vice versa. Just look at what happened to him after a pep talk from Mongul...