Not everyone in this show can rule with a sword in their hand... the themes of power and politics have a lot to do with it. Ned was a great soldier and fighter, but he couldn't play the game at all. Tyrion isn't an effective fighter, but he's a great manipulator and uses his cleverness to his advantage. And so on.. Joffrey has neither. He killed Ned when he knew doing so would cause a war and he was a coward on the battlefield and ran away. So Dany might not be able to wield a sword, but she's a tiny woman, why would she? She can use her beauty, her dragons, and her other skills to build an army herself. She proved it with the slave soldiers. She "freed" them and asked for their loyalty anyway... that ability to rouse support and loyalty is a skill.
Being able to control three dragons is a skill, whether or not she's born with it or "fell into her lap", it's a skill. Others cant do it, she can. She can speak the language because she was taught and had to learn the language in season 1. She could understand the slaver because she was taught that language from birth. She's immune to fire because she's a dragon and they had mentioned fire can't hurt a dragon earlier in the season. I wouldn't say she acts like she's all powerful, but she acts like a young woman would if just a short time ago, she was sold into a marriage with barbarians, then becomes a Khaleesi, then she gains dragons, then she takes an army, and now she's gained even more soldiers. Her power has grown fairly quickly, so it's expected she's a bit cocky.