It might be easier to offer to deed your ex the entire house and offer to pay her rent that happens to exactly equal the mortgage payments and if you can’t afford them you will leave. Perhaps that offer will make her realize that you are serious. If she refuses, well, she will learn the hard way and there is not much you can do about it.
With your coworker, I go along with the varous suggestions that you tell her it is not going anywhere; it is not coming in.
What sometimes works is the ‘I cut, you choose’ method. At least with this method, she can see that she can choose either one and so will have some comfort you are not scamming her. Something like the above may be this.
She may not UNDERSTAND it…but she will be more comforted that it less likely to be a scam.