Yes, she's a Black Sex-Link. Pretty girl! She'll lay lots of nice brown eggs for you. Some of my friends once had Black Sex-Links, and their birds laid quite well.
I agree, we need photos. However, from your description, it sounds like she could be a Black Sex-Link. They look similar to Barred Rocks as chicks. Does your bird look like this?:
Both images are from Feathersite.com