Spraddle leg often appears as a type of paralysis, could also be a slipped tendon as you said this presented when she was a few days old. Unless you're treating her for coccidiosis, you can supplement her with B-complex vitamins in her water or an oral solution of a multivitamin for chicks like Chick Booster. Considering that she's not eating well, I'd probably opt for the Chick Booster; it's loaded with a long grocery list of vitamins and minerals, including the B vitamins so important to a chicks legs and feet. A drop in the morning, a drop at night for a week, then once daily thereafter should give you peace of mind and possibly be the solution to her condition.
FYI: It's possible for nutritionally deficient parents to pass on their deficiencies to their offspring; when the chick hatches, it's already in trouble.