Genie decided to grow to giant size, but she had to make sure she wasn't detected by anyone else but Donnie. She made herself invisible to everyone else but him before she grew. Then she went to a more remote area to make sure she wouldn't be disturbed, leaving a trail for her new boyfriend...
Donnie continued walking until he saw something in the grass that made him stop in his tracks. It was a giant footprint!
It had to be 5 feet long, and looked like it was made by a bare foot. There were more prints leading away, and Donnie instantly followed them, running all the way.
Finally Donnie emerged into a clearing which was mostly occupied by the 30 foot tall genie, lying in the grass in a crude cloth bikini made from sails. She was fast asleep, or at least looked that way.
Donnie stood there, gazing in awe at the giantess.