Better yet, I'd suggest that as soon as one of her ex-in-laws begins discussing ANYTHING about their family that Donna simply say: "I care about you, but I cannot be part of your family drama. Please change the topic immediately or I'll need to stop this conversation." Continuing to expose herself to the family drama is nothing but harmful. However, Donna does not seem to be in a place for whatever reason to take this step of setting a clear boundary and letting go of that part of her life.
OT, my best friend has done exactly that recently. His wife left him 8 months ago but he still goes to dinner with his in-laws and recently he told them that he loves them and wants to keep in touch but does not want to hear about his ex. They responded very well to that.
