Lori - I have also had clients who put unused EBM in a sucked bottle back in
the fridge and give it to the baby at a later feed.  The babies seem to be
fine!  However, when I learn of it I suggest feeding the EBM in very small
amounts, filling the feeding bottle from a storage bottle.  Any unused milk
in the feeding bottle should be discarded within an hour because of
contamination from the baby's mouth (if mom does not want to waste the
"liquid gold", she could wake the baby to take the dregs an hour later!).
The storage bottle (untouched by the baby's saliva) can be put back in the
fridge and the milk can safely be used any time in the next few days (EBM
will keep in the fridge for 8 days).

Pamela Morrison IBCLC, Zimbabwe