Eek sounds tricky! I've got 3 boys and understand how frustrating it can be, especially the copying! Really is best to laugh it off as it is only a phase (sorry not helping eh!). Unfortunately if you shout you're just giving her a reaction which, for some strange reason, littl'uns find very satisfying! Kill her with kindness and distract, distract, distract!
I'm sure someone will be along in a moment with more useful advice. Also you could try posting this query on the 'Parenting' board where you'll get a much wider audience and lots more advice!