Rock week and Janet sings "Sweet Child O' Mine" by Guns'N'Roses:
Added 22/10/11: 
Recent comments about the above video:
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Molly:
November 1, 2011 @ 7:17pm
"oh my god! Janet devlin so deserves to win the x factor"
GT:
October 24, 2011 @ 3:51pm
"Sweet Child O' Mine sung beautifully and with a harp for support - genius! Its Riverdance meets Guns'n'Roses, in a good way!"