Is Sister justified in moving out and into the Post Office? Why or why not?

Throughout the story "Why I Live at the P.O.," Sister describes the difficulties that she has with her family. She believes that Stella-Rondo has stirred up all kinds of trouble for her and has turned the family against her, which is why she ends up moving out. In Sister's eyes, she is perfectly justified in moving out because she believes that everyone has been turned against her through a series of lies and trouble that Stella-Rondo has created for her, and that she has been unable to resolve with her family members.
However, as a reader it's important to remember that the entire story is told through Sister's point of view. The rest of her family lies and miscommunicates with each other all the time, and they are constantly blowing problems out of proportion. The reader is hearing an account from a biased narrator that might very well be subject to the same faults. The narrator ends her tale by saying,

But here I am, and here I'll stay. I want the world to know I'm happy. And if Stella-Rondo should come to me this minute, on bended knees, and attempt to explain the incidents of her life with Mr. Whitaker, I'd simply put my fingers in both my ears and refuse to listen (Welty).

This calls into question Sister's reliability. The reader should wonder whether or not she really is truly happy, or whether she is deceiving herself just like the rest of her family. The fact that she only tells her side of the story, and says she would refuse to listen to her sister if she tried to come explain herself, should make the reader question exactly how justified she really is.
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