Yep.. As you described to me the membrane sounds like a shrink wrap. This happens sometimes, mostly due to low humidity levels.. Sometimes just because the egg has a really tough membrane, and sometimes it is just a failure to thrive.. However, since you said your chick had started zipping, and it hasn't progressed due to the membrane.
But remember as you are helping it, if you run across blood or yolk, STOP and put back in the bator.
Or you can just wait and see what happens. But if she has been zipping for over an hour, and it has been atleast 24 hours since she pipped, the you are at the point that I try to help.