So this is how it goes:
01. Hawkins Lab planning on taking Sarah
02. They use Kali that actually already succeeded the experiment and test her
03. Kali made Hopper see Sarah died
04. Hopper left
05. Sarah is still alive
Sarah Hopper daughter of Jim and Diane Hopper died at a very age because of cancer. But, I'm not sure. I thought that Hawkins Lab wants to use Sarah as an experiment (maybe number 009, 010, idk). At that time, (maybe) Kali's experiment just succeeded. To test her, they use Kali to made the Hoppers see Sarah died. While in fact, she's save and sound.
When they left, Sarah is in Hawkins Lab. Hopper cried at the stairs of the hospital, which we later see in Season 02 is the very same stairs as the ones in Hawkins Lab. So, Sarah was taken care in Hawkins Lab and was taken from them at Hawkins Lab too. Ironic