Theo — Bargaining
Assigning Theo the stage of "bargaining" is a little murkier, but it still makes sense when you take into account her unique ability to innately see and feel things — like the past, emotions, etc. — when she touches objects or people. By using her supernatural gift, you could say Theo is bargaining for a better outcome for her and her family. In the case of Nell, for example, Theo begs both Hill House and the universe to give her an answer as to why Nell died after touching her sister's dead body and feeling a hollow, suffocating emptiness.