While the rest of Paheli’s advice is excellent, this part is not going to work. Anybody will see through it. The problem is the complete falseness of it.
What she needs to do is be straight, honest, decent, respectful and courteous to her saas. Treat her like a human being. Even if she does not reciprocate. At least then she can stand firm in her own correctness of behaviour. Being a tattechuk or chamchi will just be more BS. Enough with all of that.