There is a basis for Cynthia and Carol in Diane's waking life - DeRosa/#12. The answer lies in her function: to serve as a contrast to the object of obsession, to serve as a more practical or suitable choice over the object of desire... - (Neely O'Hara)
The neighbor Diane's real lover?
Did anyone notice that the woman who lives in apt #12 of Sierra Bonita is a lesbian? Notice the way she is checking out "Rita" while standing in the doorway. Plus, she carries herself in the stereotypical "dyke" style, with her rough/tough image Rosie O'Donnell looks. My opinion is that Diane and this girl are the ones having the lesbian encounters and not Diane and Camilla. After all didn't Diane originally live in apt #12 with the lesbian girl, before moving out to apt #17. Diane is only substituting Camilla in place of the lesbian lovergirl to fulfill her sex fantasies. Diane imagines that it's Camilla who says, "we can't be doing this anymore". Thus driving Diane deeper into her jealous, delusional state. Camilla was never there. - (FilmflamMan)
I think Diane and DeRosa definitely had a serious relationship; it was evident from their interaction and dialogue. Also, DeRosa and Camilla's similarity cannot be ignored. It seems like DeRosa is a more 'plain' version of the beautiful Camilla. Hence, I contend that, knowing she could never have Camilla as she desired, Diane went after DeRosa as a substitute. During their perceived relationship, Diane still occasionally got down n' dirty with Camilla. When DeRosa figured this out, that's when they broke up. - (Cuban Nightmare)
I used to think that Diane had basically done to the other woman what Camilla had done to her. They were together, then something better came along (Camilla), Diane dumped the other woman and went with her. Camilla ends up doing the same to Diane. Diane is so hurt, but also a hypocrite, therefore adding to her confusion and pain. - (akin-2-grieve)
Related: Camilla not Diane's lover?
Regarding the lamp lady thing, I see a similarity in Diane's actions and demeanor in this scene as well as some other scenes. Diane seems forceful and has a sense she is in control in these scenes:
1. The scene on the couch. Diane is the forceful one.
2. The scene at the doorway, Diane is controlling Camilla, making it hard for her.
3. The scene with the lamp lady. Diane is annoyed and short with the lamp lady.
4. The scene where she contracts with the hit man "More than anything in this world".
I think these scenes go together in this order and the lamp lady is Camilla. The thing missing in this story is Diane actually kicking Camilla out. Well we have another scene showing just that. - (beth elms)
De Rosa was into something sinister in the pilot/series thus the evasive looks and strangeness. I believe there is some connection between aunt Ruth and De Rosa because of their similar clothing and checking of an apartment they are leaving or recently left and is occupied/to be occupied by Diane/Betty. - (richdubbya)
Tangled identities - (Darklite)
I'm going to hit you with something. DeRosa is not DeRosa. And Diane did not switch into #17. There are a number of clues that support this theory:
Possible connection to Herb shouting out "Dan... are you alright?"
My theory is that De Rosa knocks on the door and says,
"Diane, are you alright?" at the same time that Diane is asleep and in the process of dreaming the scene in which Dan dies.