Which reply would be better to a women who was texting my husband?

Just write a simple message like this: "If I find out that you're sleeping with my husband, we are through. You can have him and believe me, he will do the same thing to you next year." Maybe this sounds too mature but believe me love, it will take the fight out of her. She wants you to be bitter and angry. But kill her with kindness and see how fast she stops taunting you.