Hello, Your 3 year old daughter cut her eyelid on a metal guitar string, which resulted in bruise and minor swelling. It is important to get medical attention for all major eye or eyelid injuries and problems. Since the eye is easily damaged, these conditions can lead to vision loss if left untreated. An injury to the eyelid may be a sign of severe injury to the eye itself. Gently apply cold compresses to reduce the welling and stops the bleeding .Do not apply pressure to stop the bleeding. If there is pooling of blood in the eye, it would be best to cover both of the eyes with a clean cloth or sterile dressing. Rinse with water. After washing the eye carefully apply a thick layer of bacitracin, mupirucin or other anti bacterial ointment on the eyelid. Following which a patch can be placed on the eye. It would be best if you do not apply Band-Aid. I would suggest you to consult your surgeon in the ER immediately for further assessment. Hope this helps. Thank you.