Flintrock:
It is obvious that your Aunt MUST be losing blood if she required 4 pints and continues to require blood. IF all obvious things have been checked... wounds, colon, urine,etc, then the only possible place she is bleeding from is her abdomen. Next step should be an exploratory laparoscopy to look at her liver, pancreas, etc. and see if there is any blood in the belly. I wish her all the best.
Good Luck,
CancerDad