She is an unscrupulous fortune hunter out to profit from the cryptids she finds. She sabotages your kite surfer, then appears at the end to try to kidnap Bigfoot.
(see related question)
cryptids island on boat then heilcopter
You get the Island Medallion after you prove the existence of three of the four cryptids, and rescue Bigfoot from the evil Gretchen Grimlock. (see related question)
you don't, you wake up in his mansion after being attacked by Gretchen Grimlock
When you get the Kite Surfer from the kite shop, go try it out at the Cliff Park (far left).
There is no way to avoid her attack. You are saved by Mews and taken to his mansion, where he has a museum dedicated to the mysterious creatures (cryptids) of the world.
Once you get the surfing kite, you will be attacked by Gretchen Grimlock and rescued by the Mews copter. At the Mews mansion, review the videos on cryptids in his museum and you can use the helicopter to go in search of proof.
When you catch Gretchen Grimlock's helicopter, jump onto it from yours, then click her gas cap and fuel will start coming out. Cut loose the line to Bigfoot's cage with your gardening shears, and you both float safely down on the cage's parachute.
After you only get a footprint photo from the Himalayas, Mews decides that it is too difficult to track the Yeti. When you prove the other 3 cryptids, he sends you in search of Bigfoot, and you have to rescue the creature from the evil Gretchen Grimlock.
To win the island, you must find the proof that confirms the existence of three legendary cryptids : Nessie of Loch Ness, the Chupacabra, and the Jersey Devil. Then you have to rescue the 4th creature, Bigfoot, from the evil plans of Gretchen Grimlock. (see related solution question)
When you have confirmed the existence of three cryptids (all but the Yeti), the final location is the Pacific Northwest. You will go there to follow Bigfoot back to his cave home. But unfortunately, you will also have to save him from Gretchen Grimlock. (see related question)
You save him from Gretchen Grimlock by gettting close to her helicopter, jumping across to it, opening her fuel cap, then cutting loose the Bigfoot cage with your shears. You will float down on its parachute.
Bad girl? When Gretchen Grimlock carries Bigfoot away, follow her helicopter then jump over to it, open her gas tank, and jump down to cut loose the cage.