How could they know the demerol was injected two minutes before she died when it looks like she was dead for many hours before anyone noticed.
Maybe the drug couldn't circulate in the body and stayed near the injection site because she was dead.
Didn't Perper say that her body was still warm when she arrived at the hospital? He was commenting on the efforts to revive her and why they thought there was a chance to bring her back, I believe.