Don't trap your fox unless you will shoot! All you will do is make her trap proof, and still want to eat chicken. If it's a vixen with kits, she is teaching them about chicken too. It's illegal and cruel to relocate a fox too. Electric poultry netting should keep her away from you birds when...
Your fox, or whoever, will return until either you trap and shoot, or just shoot. Meanwhile keep your survivors on lockdown 24/7 or you will loose the rest of your flock. Again, so sorry. When a fox killed ten of my hens one afternoon several years ago (in view of a workman who did nothing!)...