Just leave her be. It usually takes chicks 4-12 hours to finish hatching after they first pip, but in my experience, they can go as short as 10 minutes or as long as 24+ hours. If you open up the incubator to assist, you'll risk disturbing other eggs, reducing the humidity (causing the membrane to dry out), and may cause more harm than good with the egg being assisted. I would just keep a close eye on the egg; if the membrane turns white and stiff, you can rub some water on it to soften it, and if no progress is made by tomorrow afternoon, you can slowly chip away some of the shell. Watch out for blood vessels, and stop if it starts bleeding too much. Good luck!