A feral cat had kittens in my back yard under a board.. about a week ago.. I want to try to get them to a safe place but will she abandon them if I try to get them? She hisses at anyone that comes by.

Maybe more than likely she will try to hide them

Maybe just try to bulid her a small shelter closer to the house so that you can keep an eye on her, and put food in there with maybe some straw and insulation for the inside. If she knows there's food there, she might decide to move her babies in there to keep them safe and warm, htat way you're assisting in keeping her safe, but from a distance so she can do her thing.