During daddy's trip back to hometown in July, the three girls slept together. When MS saw ES & LS no longer wearing diapers, she told me that she does not want to wear diapers too before I put on the girls to sleep one night. Peer's influence did make a great impact.
From then onwards, she is diaperless at night time too. Just as simple as that, she is not wearing diapers during day and night now. On and off, she still wake up during midnight for pee.