Unfortunately there is no way to untangle the umbilical cord when it is like that. The only thing you can do is cut it off about 1/2 inch from the belly Once you cut it tie off close to the belly with dental floss.

If the baby has ok weight just leave her and let her shed.

If she is very thin then you can mix up the yoke from a chicken egg and load it into a syringe. Take a fairly large needle (16-18 gage) and send it up the umbilical cord and inject it into the snake (you have to do it right to get it into the right spot). Once you fill up her belly you can tie off the umbilical cord to keep all that yoke inside of her. I don't recommend doing this unless you feel confident doing it. It's easier than you think if you go slow.

Good luck,
Corey