Beth Merritt is one of the original 33 background survivors. "Pilot, Part 1"
She was present on the night of the crash on waiting to get rescued. ("Pilot, Part 1")
She also saw the trees shake and heard the sounds of the monster. When Hurley started building the Golf Course she could also be seen in the background.
In addition, when Boone died, she was there at the funeral with all the survivors. On the Island, she always was giving food to the survivors and collecting wood for fire.
She was there on the day when Kate and Sawyer returned to the Island from escaping from the "Others" camp. She was there when she heard Hurley making a speech to fix up the DHARMA van. ("Tricia Tanaka Is Dead")
When Kate and Jack returned to the Island from escaping from the the Barracks, she was there to witness Juliet arrive on the beach.
When Karl was making his speech that "The Others" are coming to the camp to take the any women with babies, Beth was there with all the remaining survivors. ("Greatest Hits")