why does suzanna have no bones in her wrist and what does wrist banger mean??

She does have bones in her hand/wrist, but she thought she didn't (due to her mental illness).
And a wrist banger is basically someone who bangs their wrist on things, to cause bruises. It's a form of self harm.

Susanna undergoes a period of depersonalization, where she claims she has "lost her bones."