I had an IUD like that once years ago and I remember my partner of the moment wincing in pain when he encountered that "thread," although it's not really a soft thread-- at least mine wasn't-- it's more like one of those stiff nylon threads that they use to put labels in the backs of shirts that stab you in the back of the neck.
But ask any of the HD guys on here what they would do in like circumstances? I'm guessing they'd suggest a different method, ask her to ask her GYN if there's something that can be done? Not just say, "Okay no sex."
