I sympathize, because we have someone in our lives who makes plans, then comes up with the lamest excuses to cancel at the last minute. I think, instead of calling her out on it, which will only cause more phone calls with more excuses and pleas for "don't be mad", you just have to teach DD to know that when she makes these plans, take them with a grain of salt. Don't expect they will be followed through with so when she actually does, it will be a nice surprise. I used the line with my DD "Well, we might visit/go somewhere/have fun with person, but it isn't definite. It sounds like your MIL has some issues she needs to deal with, but that isn't your families issue. You have to focus on how your family deals with her empty promises. Good luck because that makes me angry when a child is disappointed by someone they love.