How you handle a cold daughter in law won't differ from how you handle anyone with those tendencies. The issue here is not that she is fake and unloving and cannot rationalize why she's that way, but rather are you OK with her behavior? You know that you cannot change anyone or what they think or feel. In that case, you focus on your own interpretation of the situation and what you feel as a result.
Do you really need her acceptance and love to know that you're a worthy individual? Not really. You've lived all of your life w/o her until she married your son. For whatever reason she feels what she feels. Even if he is influencing her, you're not responsible for that. She is. She decides what to feel, what to believe and how to act. She's an adult.
As far as how you handle or treat her- you've already done that. Continue to be civil with her. There is no reason for you to feel animosity towards her. Perhaps with time, she will come around to see things for herself w/o external influence. Until then, you accept her the way she is if you are willing to and go with the flaw. Try not to personalize her behavior.