nicolae

child thrive on routine and dependance, when changes in a childs routine happens the child becomes uncomfortable and scared. her living with grandma and grandad was a major change in her life and routine, that is the reason she dramatically changed, and again also her routine that she settled in with grandma and grandad was changed again, therefor making her act out like you said. they key word in what you do next is ROUTINE, she needs to get back in a routine again, same bathtim, bedtime, teatime etc etc.
about the tanstrums, when she is having a "strop" you baisically ignore her completly, move anything out of her way that she can hurt others with or hurt herself and ignore her, but still keep an eye on her of course. children throw tantrums to get lots of attention, weather it be good or bad. leave her to it, and evenually she will stop, she may come and say sorry, and get back on with whatever she was doing.