I understand now how to work with the iframes. Find the frame with FindElement with a wait, then enter the frame with FrameEnter and then find the element using FindElement again, using relative Xpath. Working script below, thanks again for your help.
Func DisneyLogin()
Local $sElement, $sButton, $sXpath, $sEmailInput
_WD_Navigate($sSession, "https://disneyworld.disney.go.com/login/")
_WD_LoadWait($sSession, Default, 10 * 1000)
_WD_WaitElement($sSession, $_WD_LOCATOR_ByXPath, $sXpath)
ConsoleWrite("Frames Count=" & _WD_GetFrameCount($sSession) & @CRLF)
ConsoleWrite("TopWindow=" & _WD_IsWindowTop($sSession) & @CRLF)
;Locate email frame element
$sXpath = "//iframe[@id='oneid-iframe']"
$sElement = _WD_FindElement($sSession, $_WD_LOCATOR_ByXPath, $sXpath)
_WD_FrameEnter($sSession, $sElement)
;Locate email element
$sEmailInput = _WD_FindElement($sSession, $_WD_LOCATOR_ByXPath, "//*[@id='InputIdentityFlowValue']")
; Set email input element's contents
_WD_ElementAction($sSession, $sEmailInput, 'value', "someone@somewhere.com")
; Locate continue click element
$sButton = _WD_FindElement($sSession, $_WD_LOCATOR_ByXPath, "//*[@id='BtnSubmit']")
; click continue element
_WD_ElementAction($sSession, $sButton, 'click')
_WD_LoadWait($sSession, 2000)
;Locate password input element
$sElement = _WD_FindElement($sSession, $_WD_LOCATOR_ByXPath, $sXpath)
_WD_FrameEnter($sSession, $sElement)
$sEmailInput = _WD_FindElement($sSession, $_WD_LOCATOR_ByXPath, "//*[@id='InputPassword']")
; Set email input element's contents
_WD_ElementAction($sSession, $sEmailInput, 'value', "password")
; Locate continue click element
$sButton = _WD_FindElement($sSession, $_WD_LOCATOR_ByXPath, "//*[@id='BtnSubmit']")
; click continue element
_WD_ElementAction($sSession, $sButton, 'click')
_WD_LoadWait($sSession, 2000)
EndFunc