Her color certainly looks like one, but she has lightly feathered legs, which pretty much rules out hatchery bsl. I was thinking she must lay darker eggs if the OP thought she was a Marans. She could easily be a someone's homemade BSL using a cuckoo Marans instead of a barred Rock, but cuckoo Marans aren't as likely to have feathered legs as other varieties. But her color does lend itself to being a mixed breed.
