It is interesting that you have a family bible with an IREY surname pre 1800.In two message that you have posted to this site you list Margaret's potential birthdate as both abt. 1764 and 1777.
Based upon information currently available regarding the IREY family and depending upon which date is more accurate, Margaret could either be a possible daughter of Philip IREY Sr., the daughter of one of Philip IREY Sr.s sons (John, Phillip Jr., Samuel) or, she descends from a previously unknown IREY.
In any event, this is interesting news to me, and most likely to about 30 other IREY cousins researching this remarkable family.
Current information originates the IREY's in Loudoun County, Virginia who later migrated to both Columbiana and Marion County's, Ohio.Wayne County, Ohio appears to be midway in a direct line between the two. It is very likely that the Loudoun County, Virginia IREY's began in Pennsylvania.
Does your bible pinpoint what part of Pennsylvania?
Current family information includes several Margaret's, however none of them match the approximate dates/geography/spouses, at hand.