Kitten might not have been thoroughly socialized. IT would take time, but you might be able to do it. Otherwise, taking it back to shelter is a sure euthanization. IF you had 2 though, one that was 100% socialized, it would help socializing the other one much more quickly.
You should have 2 cats anyway. They are healthier and happier when they have a mate.
I didn't get her from a shelter, she has been fostered thru an agent of a local rescue agency and has been in her household since June..........