Following on from Lonk's suggestion, here's a UDF to do the job.

Note, no type checking of variables, use the optional delimiter if you have @CRLFs in the data.
Code:
Function udfStrInArray($aArray,$sSearch,Optional $sDelimiter)
	Dim $iIndex
	If Not VarType($sDelimiter) $sDelimiter=@CRLF EndIf
  
	$udfStrInArray=(-1)
  
	$aArray=Join($aArray,$sDelimiter)
	$iIndex=InStr($aArray,$sSearch)
 
	If $iIndex $udfStrInArray=UBound(Split(Left($aArray,$iIndex-1),$sDelimiter)) EndIf
 
	Exit 0
EndFunction


This returns the array element that the (sub)string was found in, or "-1" if not found.