She's scheduled to speak Friday. Bush also will join first lady Michelle Obama on Saturday, the ninth anniversary of the attacks, for a memorial service at the crash site.
Next year, on the 10th anniversary of the terrorist attacks, officials plan to gather at a permanent memorial plaza that is under construction. It's part of a planned 2,200-acre national park.
Flight 93 was en route from New Jersey to San Francisco when hijackers seized control. The 40 passengers and crew fought back and the hijackers responded by crashing the plane about 60 miles southwest of Pittsburgh.