Scans cleared the Roosters captain of a fracture after she left the field early in the second half of the 32-18 win over Parramatta on Sunday.
Coach John Strange named Kelly to start in Sunday's match at Allianz Stadium in a boost to the side's hopes of avoiding a third-straight exit in the semi-finals.
Kelly's fellow centre Jess Sergis and playmaker Tarryn Aiken have both been named in the extended squad, so they could overcome respective knee and shoulder injuries in time to play.
The third-placed Knights welcome prop forward Rima Butler back from a knee injury to face the Roosters, pushing Tayla Predebon to the interchange.
New Zealand international Nita Maynard returns from an ankle injury to the Knights bench, forcing Evie Jones to 18th player and Evah McEwen to the extended squad.
Elsewhere, Cronulla have promoted Tegan Dymock to the starting side for their semi-final against Brisbane after prop Holli Wheeler accepted a one-game ban for her high shot on Sarah Togatuki.
Rhiannon Byers and Brooke Anderson have both been named to start in the Cronulla forward pack, despite leaving the round-nine loss to Wests Tigers during the second half.
Minor premiers Brisbane have named the same 17 that defeated St George Illawarra in the last round of the regular season.
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