How old is your daughter? I've found that all the same techniques you would use for normal separation anxiety work. Warn that transition is coming, keep goodbyes brief, create a routine, don't talk about "missing" her.
Our routine is basically hug incoming parent, brief conversation, hug outgoing parent, leave waving goodbye and saying "I love you!" Instead of saying "I'll miss you," I say, "Have fun with Daddy!"
My XH tends to sabotage goodbyes because it gives him an ego boost to have DS1 be sad to leave him, but most of the time we stick to it so DS doesn't have issues.
Re: Saying goodbye and meltdowns
Our routine is basically hug incoming parent, brief conversation, hug outgoing parent, leave waving goodbye and saying "I love you!" Instead of saying "I'll miss you," I say, "Have fun with Daddy!"
My XH tends to sabotage goodbyes because it gives him an ego boost to have DS1 be sad to leave him, but most of the time we stick to it so DS doesn't have issues.