please click here and practice: http://translate.google.fr/?hl=fr&tab=wT#fr/en/un%20chien%2C%20une%20chienne
True, as in most modern languages, hundred years ago it was a different story. But, in this specific case where the dog is explicitly a "chienne" you have to, in one way or another, establish that it is a female dog. Using a pronoun, I would opt for "she", using a noun, people suggests ❤❤❤❤❤, which to me sounds a bit vulgar, I might be wrong here.
I don't understand and this puzzles me somewhat. "Une chienne" is clearly feminine, and "c'est" in front of an article may very well mean "She is", so why is "She is a dog" considered not correct, especially when I hovered over the statement to be translated.., and it indicated that the correct translation would be "She is a dog???