Change your tone of voice when she has been naughty so she can clearly differentiate between you telling her off and the times when you praise her or speak normally. Holding her hands down whilst you are speaking to her will stop her lashing out and reaffirm your authority. The naughty step can work at that age, but you may find yourself repeatedly sitting her back there, which is fine as long as you tell her beforehand why she has to sit there, for no more than a minute though.
Acting over the top and loudly does work as a shock technique, basically "look I can have a bigger tantrum than you" - my husband has perfected this and it usually ends up the two of them giggling and all anger and tantrums are forgotten.
This might be a lot tougher for you, as she may have seen behaviour from others that you're not aware of, or picked up on things around her that have made her feel unhappy and lash out. It won't change overnight but if she's settled in a loving home and gets lots of love and praise from you, and of course she'll get a little older, this behaviour will become less frequent.
Consistency is the key - keep the routine, i.e. if she hits you, go over to her, hold her hands down to stop her doing it again, tell her (in your different tone) it's wrong to hit others and now she has to sit on the naughty chair as punishment. If her language is good enough ask her to say "sorry" after she's sat there for 1 minute and then have a cuddle, and all is forgiven and you can carry on. Works for us, my daughter is now 2� and rarely sits on the naughty chair now.