You gotta level up your healing skill till 5 if im not wrong, and after healing her, dont go hunt immediately, wait so she can recover, then you go and hunt.
i was also stuck on that part, i choose to just wait with her inside the cave out of curiosity and i got it.
its an mix of luck and skill, like in 4/20, after it hits 5 am, leave the camera on freddy and DO NOT PULL IT TO CHECK ON HER, and just use sound to know what is happening around you.