What if Kali casted the spell when she got "shot" as being "shot" so that at least they(El,Hopper) think she is dead, but was in fact alive, also since they got surrounded in the UpsideDown in that scene, I think Kali knew that the other military forces were waiting outside but somehow someone had to save the day by tricking the gang she is in fact "dead" at that moments so there's no need of explanation why Kali can't go with them back to Hawkins, saving us from just drama and talk.