Johnson has featured in 13 games this season for the Eagles having signed for the south Londoners this summer.
Having already described Johnson as "a fighter and a leader," manager Dean Davenport has now said: "We are delighted AJ has agreed to stay with us. She has proved herself over and over again this season so far. We only expect more good things to come from her."
Speaking after putting pen to paper for the Eagles, Johnson said: "I’ve settled in at Palace quickly and I’m really enjoying my football here. I’m excited about my future with the club and I’m looking forward to seeing how we can grow and what we can achieve."
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