What Causes Soreness In The Finger?

Daughters middle finger red, swollen and sore from middle of finger down towards wrist. maybe 2 inches. red streak. warm to touch. went to er where they ran blood work and x rays, but could find nothing and released her after given antibiotics in iv and prescriptions. they poked it, but only blood came out. they were expecting pus. no cut, no bite, not injured...been 2 days. red streak gone with antibiotics. any o
pinion would be helpful. they suggested hand expert.