I think that you are talking about the truth ending (the first one), for it you need to talk to Nala multiple times throught the game, if you dont do it, she wont help you in the basement and you will get the worst ending (rebirth ending).
As for the artifact ending, i think, that it is indeed bugged, after collecting 3 souls and refusing to go in the basement game just freezes at the black screen.
Basically only talk to the characters found around the game for nessecity and nothing else. (talk to Nala, get the key, never speak to her again except for when you need to later ask her to play the Piano. When she asks about if the worst happens, just say you would run. If you treat it like a speedrun you should trigger the Rebirth ending no problem.
If you mean confronting her in the piano room? It's not avoidable nor does it impact the ending. The only times there is optional chatter with her is after getting the key to the southwest section of the house and after surviving Mika the first time. Anything more than that is optional dialogue with her. Avoiding it and making sure to resist being prey whenever possible should trigger the Rebirth Ending.
