basically that girl she loved is already dead and she went mental and imagined her still alive and with her.
She's not imagining her alive, she knew that the girl she likes is already infected, she was just retelling her dream to the infected girl. Though I won't deny that she has a loose screw on her head.
well love does drive people mad and if you are talking about the end of the world can't blame her for that but still i kinda like nomal yuri love story with no bad end
i don't understand the ending at all(⊙…⊙ )