YJ02
Well Known GateFan
She was killed when she hit her head on the meteorite containing the egg when somebody pushed her. She was dead, not disappeared. She is compelled to protect the egg for some reason, but I believe Melanie floated up from the bottom of the lake intact when Julia tossed the egg into the lake. Like a minute later, Melanie appeared in the water.
Clearly the egg/dome has something to do with her re-appearance. Not a coincidence