"Yes, she is a girl."
Translation:Ja, hun er en pige.
Don't worry, you're not being stupid, it's just the grammatical gender of the word. 75% of nouns are common (n-words) and the rest are neuter (t-words). Rule of thumb is that words relating to animals and people tend to be common (some notable exceptions are et dyr meaning "an animal" and et menneske meaning "a human/person")
You have just to learn the en- and et- substatives. It is the same in the other scandinavian languages, and yet the same substative can get different 'articles' in the different scandinavian languages. That is an 'et' Danish word may well be an 'en' word im Swedish and the opposite of course.