The only way I was able to beat that part was to examine the door switch (to get the zombies started), hold Amy's hand, sprint to the body with her, scan the body, and then leave Amy there as zombie bait while I ran around back to the door. As long as you can reach the level exit before Amy dies, it counts as winning.
Probably not the solution the devs had in mind, but it's the only one I've found that works on Hard mode.
I actually like that part lol I was like "screw Amy I'll just grab the sample and go open the door" while sprinting them zombies. They stop and drain her energy but it's a few seconds before you open that door and finish the chapter. --- If Destiny Interferes With Reality, One Man's Determination May Merely Be What Is Determined By His Fate.