She is just riding the ups and downs of her emotional roller coaster. It happens here all the time and just takes a little time to get used to it. Just think about it from your side....You go see her and no matter what you are going to act happy. So she's you being happy...so there is no way she is going to act unhappy. Over time as you become stronger in your conviction and inner strength the happiness doesn't need to be forced and vice versa..as she realizes what has happened do to her actions...she gets depressed and it is harder to put up the charade of happiness.
You are doing excellent overall. I would also make sure that you check in with the kids regularly and volunteer to spend extra time with them since mom is away. Don't think about what she is doing, but instead focus on being a dad above and beyond what she or her mother would expect.
