She was played by Tina Louise, who also played Ginger Grant.
Eva Grubb is an insecure "Plain Jane" who left civilization and headed to the island to be alone for the rest of her life. She was unaware that the island was actually inhabited, and she would learn this when she runs into The Skipper and Gilligan. Eva tells Skipper that they can have the boat, as she had no plans of ever leaving the island. She then told Skipper and Gilligan her story; that she wanted to get away from everyone, especially men, after she was stood up on a blind date. Eva saved up to buy a boat so she could get away from civilization, and she handed Skipper the keys. After introducing Eva to the rest of the castaways, the group planned to take Eva with them off the island, but they had to keep it secret from her, figuring that she was dead set on remaining on the island. Their assumption turned out to be true, as Skipper, Gilligan, and Professor noticed that the spark plugs were missing, and at that moment, Eva appeared and stated that she took out the spark plugs after Gilligan told her that they planned to take her off the island with them.Ginger and Mary Ann come to the conclusion that what the insecure Eva needs is a makeover to build her confidence. The pair, with Mrs. Howell's help, completely change Eva's look; giving her a brand new dress and dying her hair red, and the result has Eva being a dead ringer for Ginger, much to the surprise of all of the women, most of all Ginger. Eva doesn't believe that she could actually look like Ginger, until she looks at herself in the mirror and notices the resemblance, especially without her glasses (despite Eva being unable to see without them). With her brand new look, Eva gains a load of confidence, and later made an impression on Gilligan as well. She later returned the spark plugs from her boat to the group, and was now eager to leave the island and return to civilization.
Eva listens in on a conversation between Ginger and Mary Ann, which is about how Eva will adapt to the world with her new look. Ginger stated that as Ginger, Eva has poise and sex appeal, but she lacks that as Eva, and she could expect more of the same when she gets back. Ginger said that there's only one Ginger Grant, and that had Eva's wheels clicking.Later on, Eva meets Ginger to thank her and the others for what they've done for her, but that moment, she knocks out Ginger with a coconut. After her heel turn, Eva tied up and gagged Ginger and revealed her villainous plan to get off the island with the rest of the castaways as Ginger Grant, leaving the real Ginger behind alone. She then rejoins the group at a farewell gathering, and to keep them from finding out the truth, she kept switching dresses during the gathering. While dressed as Ginger, however, Eva's glasses are broken by Gilligan while the pair danced, and later on, the real Ginger appeared and foiled Eva's plan. After being caught, Eva showed remorse for her actions and left in embarrassment.
At the end of the episode, the group realized that Eva was gone, and so was her boat. Figuring that she had left them, the group rushed off to find Eva, only to find a note she left revealing that she had indeed left the island. As the note stated, the evil Eva expressed pride in fooling the castaways into believing that she was Ginger and is now on her way to start her career in Hollywood. To add insult to injury, Eva signed the note, "The new Ginger Grant."