A.,
I have 6 children ranging from 4 to 17. A few of them are extremely sensitive. Two of those react to frustrations with complete anger and fits. My oldest son (now 13) was an extreme challenge. I had to really learn how to speak to him in a matter of fact tone that was not sounding irriated or angry (just the way it is type tone). Not that this completely cured him. Every time something didn't go his way he'd be upset, BUT he wouldn't listen AT ALL if I had an irrated or angry tone. If it is going to ever sink in, it has to be in a matter of fact, yet loving tone. They need to understand that what they are doing is wrong, but mom's love doesn't change. My extremely sensitive son was also one who seemed insensitive to others. He would dish out yelling and rudeness 10 fold of what he could take.
For my 4 yo, I make sure that I lift him up to my eye level (or bend down to his) and have him look me in the eye. I will then explain what I need to explain. If she is touching something you have asked her not to touch, you tell her, "Mommy has asked you not to touch that and it is very important that you listen to mommy." Make sure she is keeping eye contact. They don't do this very well so I would be constantly stopping to say, "look at mommy" (or look at mommy's eyes). I would also ask her to repeat what you just said and maybe add in, "now what are you going to do?"
This is not saying that from then on she'll never do it again. At this age their attention span is short so she may forget again the next day or hours later. You just repeat the process. If you see her touching the item later on you can say somthing like, "oh! Remember what we talked about earlier about you touching that? What did you tell mommy you were going to do?" If she forgot, gently remind her and ask her to repeat what you said again. If she remembers, that is good. It means it is in her long term memory but she just forgot at that moment and you helped her to remember.
For sensitive children, tone of voice and facial expression has a lot to do with how effective you are with them. You don't want to give a facial expression that is gleeful where they think you're not serious either, but an angry one will shut them off to listening.
Remember that we can get overloaded with life too and sometimes it is hard to keep that calmness. I can lose my patience and sound irritated. I can see right away that my response only made things worse though. If I can gather myself, I will apologize for reacting as I did, but remind them in a better tone what they did wrong. No one is a perfect mommy that says everything just right all the time. Don't beat yourself up for getting frustrated. Children are challenging. I feel like I could have my psychology degree after I'm done raising my kids.
M.