D.S.
you didn't say what discipline you and your dh use(d) prior to dd going to your in-laws... but it sounds like there needs to be more consistency. but first off, her behavior is NORMAL! she is testing her limits and what she can get away with. this is such a hard time for little guys... their emotions are going crazy, their bodies, and they are learning so much... it's hard to handle! i know my daughter has many "break downs" a day... it's hard to handle! she is 28 months old.
i agree with the timeouts... decide what is most important (for us it's hitting, kicking, biting, throwing) and give timeouts. 1 warning is appropriate at this age. and timeouts should be # minutes= # age... so 2 minutes at this age. talk about this with in-laws... it needs to be consistent across the board. your daughter will get the idea soon. my dd goes so far as to tell me her toy needs to go in time out b/c it was going to hit her. don't get me wrong she still TESTS her limits a great deal! playdates are horrible right now, because she pushes and fights over toys... i'm hoping this will pass if i'm consistent.
oh yeah, i forgot to say that there are times that i do NOT give a warning... for example if she hits me or her daddy in the face.. that is UNACCEPTABLE and i give an automatic timeout. I think it is okay to have 1 or 2 things that you have an automatic timeout policy for...
also, my dd still gets up and tries to run around during timeout... 1/2 the time i end up sitting with her and holding her there. i do my best to not make eye contact and make it no fun.
another thing... i remember hearing that when you use time-out. LET the time-out be the discipline. In other words, once they're "served" their time... quickly tell them why they had a timeout (no lectures! they're way too young!), give a hug, reassurance of your love and move on...
HTH