Where on the head is the molt still attached? Also, is her thorax deformed? Usually when the molt gets stuck at the head, their thorax will bend. Mantises that have deformed thoraxes will not eat and cannot recover from it.
You can gently tug on the molt to see if it'll come off in one piece. Otherwise you'll have to use tweezers to remove it piece by piece. Water is situational, sometimes it can make the molt harder to remove because the molt partially disintegrates.
If her mouth is affected, make sure to check if she can still move her mandibles. If her mouth deformed due to the molt getting stuck, she won't be able to eat and therefore euthanasia may be the kindest thing to do.
Picture is always helpful. Your mantis won't suffocate, they breathe through little openings throughout their bodies. Also in my opinion, don't wait. I've had more luck helping a mantis that's still molting out of it's stuck shed than waiting for the shed to harden and its to the mantis. Of course, you have to be 100% sure your mantis is actually stuck, otherwise intervening will do more harm than good!
Good luck!
