the slewed mirror, full-length, her, myself, who did this to me? (8-9)
At first Miss H doesn't even recognize herself in the mirror. She sees a "her" – like she's looking at another person before she recognizes herself. This might be madness, or it might just be plain old shock: she has become pretty strange looking over the years and she probably doesn't see herself that often. She asks who's at fault. Is it her? Her former fiancé? This seems like a pretty sane question to ask.
Give me a male corpse for a long slow honeymoon.(15)
This is perhaps the height of Miss Havisham's craziness. We don't want to know what she's going to do with this male corpse. Not at all. Nor do we want to.
Don't think it's only the heart that b-b-b-breaks. (16)
Miss Havisham's body is broken, her life is broken, and maybe even her mind. So is she crazy? We're still not sure. Is she stuttering here? Blubbering? Shivering? Trying to decide just what is going on in Miss Havisham's mind is one of the things that make this poem so unexpectedly fun.