Very few buyers for hook and line caught turtles. Your not gonna pay off your mortgage with one 20 pound turtle.... (kind of like a deer everyone adds weight onto them) So if you want her out of your yard which she probably already is why not call somebody in to get her out. Somebody with a commercial license and the know how to cage it instead of hooking it. They will already have a buyer and might even float you a couple of bucks.
Find someone who makes great soup and trade Turtle for Soup I can give you a killer recipe I got yrs ago from an outdoor Mag. The Older people may remember Cynthia Bashline who had a monthly recipe in (Outdoor Life)? magazine. I just can't be bothered killing those old boys anymore and taking all day to cook 'em .