Ferritinlevels reflect the body's amount of stored iron. If the serum ferritin is dropping (though 153 would still be in the normal range) after iron IVs, your wife may have inadequate iron absorption or may still be losing iron due to heavy blood loss: in pre-menopausal women, heavy menstruation is a frequent cause and GI bleeds are also a common cause.
Do you know what her ferritin level was before the iron IV? Have the doctors done any tests like an upper or lower GI study that would help determine if there is anything abnormal there?