whats going on?

I totally understand where you're coming from.  I spent the weekend from hell down in Chch in January last year with DHs family, I was so emotionally high strung by Sunday I cried at the airport when we were heading home. 

Michaela's uncles sound similar to your dad.  They speak aggressively to each other, they're just playing about but Michaela didn't understand that and within a day of being around them all it took was for one of them to look at her and she burst out crying and clung to me.  That coupled wih being in a new environment and Michaela became such hard work.  Having someone who she's not used to and is dissimilar to the type of people she is used to invade her environment (i.e. family staying) is probably having the same affect on your DD.

Once we were home Michaela settled back into her routine and became her lovely cheerful self again.  I hope the same happens for you after Sunday and good luck until then.