Your Grandaughter has some anxiety about the Move firstly she had to leave her school and her friends then a new House, area and school to deal with, then her Dad is away for quite a while, its a lot, I dont think this is anything other that time will heal and as she makes friends and settles in all will be well, tell her Mom not to feed into it and if the child crys its okay its a release of her feelings , let it go and all will be well. Do not read more into it, or it could make more of it in her mind.