Do we know for sure that Tryla Scott died in the episode? Admiral Quinn survived being shot with a phaser...
Quinn was brought down by Crusher when she used the high stun setting. The parasite was still attached to Quinn when in sickbay and she stated that any attempt to remove it now would probably kill Quinn. It wasn't until the mother parasite died that the parasite was removed safely.
Crusher insists that Picard and Riker set their phasers to kill since it has little effect on the creature or the host, despite the high stun setting being effective on Quinn. Remember, this is the same doctor who was willing to let a group of people die rather than get infected with a disease that doesn't kill you. When they shoot Captain Scott, the parasite leaves her body. When Quinn was stunned, the parasite remained in the host. Why would a parasite remain in a non-living host if the parasite in Quinn's body still remained when he was alive?