@sanderml,
I don't get jealous easily, but this "Telephone Tilly" (lol) is kinda asking for it. What I would do is to befriend her. Keep your friends close, and your enemies closer. Be charming. Be vivacious. Throw her off-guard. Let your husband see how gracious you are. Make him fall in love all over again with you. Irk her. Egg her on to make mistakes, say the wrong things, whatever, so when sh!t hits the fan, guess who'll side with you? ^_~ the lovely, attentive, NON-JEALOUS, awesome wife. You'll win both the battle and the war. Sun-tzu would be so proud of you!