Ummm, consider a few things.
This is all hearsay. Christie has said no such thing to you and no such thing to your DH, correct? You don’t know if it was ever said, if something like it was said but misunderstood, if something like it was said in a fit of frustration, but not meant seriously, if that exact same thing was said and meant intensely, but since repented of, or if by charitable reaction on your part, the same might be repented of in the future, providing the context for her conversion to the CC!I
Keep your eye on the ball, here. God doesn’t just want you and your DH. He wants her, and He wants her more intensely than you can imagine. Whenever possible, God expects you to go for the whole ball of wax, too. If the report is true, let the difference be that you, unlike Christie, understand how souls are won.
Keep in mind, too, that the life of your marriage depends on no one but you and your DH. If you (plural) decide to make your marriage a priority, the gates of hell won’t prevail against it, let alone a meddling SIL (or two). Trust me, they have tried. It is best that they be treated like mosquitoes in Minnesota, the inevitable downside to this lovely country you have given your life to, and not as if they were Nazi storm troopers with the power to carry you all off in the dead of night.
If moving is what it takes to keep peace in your home, by all means, move. Don’t pack up on the advice of gossip or hearsay, though. To be cut off from one’s family is like cutting off a limb. It is sometimes a life-saving operation, absolutely, but it is still one to be reserved for extreme cases.
In other words, your best course of action is devotion to your faith, devotion to your DH, and devotion to the cause of your new family’s conversion. Pray every day for your conversion, for your husbands, but also for theirs. This Christie is not lukewarm, and that is a point in God’s favor. (Don’t forget to enlist St. Paul’s intercession in this matter. He knows a thing or two about the strong-willed.)
In any case, although I am sure she must have meant well, it was not Diana’s business to pass this on and upset you. Charity requires–REQUIRES!–that you put the best possible interpretation on what Christie might have said or meant. This is no handicap, for following the Will of God is always to our greatest advantage. Proceed carefully, then, and above all prayerfully, with the best interest of all souls in mind.
This is not a battle to be won on your strength or cunning, but by the power and Will of our patient and merciful Father in Heaven and our Lord Jesus Christ, who loves each and every one of you to the extent of death on a Cross. Do not forget that. Then you will be OK.