badly behaved princess

What does one do with a little spitfire who pulls hair when she doesn't get what she wants and does the pre-emptive cry before you scold her? i didn't realise that the terrible twos have landed on me prematurely! Maeve is now in the habit of fighting with her cousin every day. Without fail. the harried grandma reports every evening that the little one is very fierce and defends whatever she is holding on to with great passion (or stubborness rather), which means pulling hair, pushing or screaming for help. For some reason, she obeys me at home and when i give her a firm look, she responds. BUT..in the gramps, it is a different story, my angel transforms and the horns sprout instantly. so disciplining her there is a futile endeavour. The family now calls her "drama queen", of course, making loud asides of "i wonder where she got that from" wink wink, snigger, snigger. sigh...