Who went in the Westing house on Halloween in The Westing Game?

The answer to this question can be found in the chapter titled "The Corpse Found." It is chapter 4. Turtle Wexler is the person who goes into the Westing house that night. We are told that she is dressed up like a witch, and her clothes underneath are bulging with all of the stuff she needs for her plan. Her plan isn't to just go into the house, but she plans on staying the night, so she has with her two sandwiches, a flask of orange soda, a flashlight, and a silver cross "to ward off vampires." Her reason for going into the Westing house is to make money. The house scares people, and Turtle goes into the house on a bet. Doug, Theo, Otis, and Sandy agreed to pay her two dollars per minute that she stayed in the house. Turtle stayed in the house for 12 minutes. She ran quickly out of the house after discovering a dead body.

At two dollars a minute, twenty-five minutes would pay for a subscription to The Wall Street Journal. She could stay all night. She was prepared.
[. . .]
Turtle hid the folded newspaper in her desk drawer, counted her black and blue marks (seven), dressed, and set out to find the four people who knew she had been in the Westing house last night: Doug Hoo, Theo Theodorakis, Otis Amber, and Sandy. They owed her twenty-four dollars.