my advice:
try verbalizing for her what she's trying to say. Of course this doesn't work when they're actually flipping out but it can help de-escalate a situation before it gets to that point.
For example:
DS is starting to get upset
"DS, are you mad?"
YES
"You want the ball?
NO
"You want the truck?"
No
"You want the XYZ?"
yes
"okay, I know you want XYZ and you're mad because you can't have it right now. we have to do ABC first. ABC then XYZ, ABX then XYZ"
I hope that makes sense.... I think the PP had it right when she talked about giving her the words. the other thing we did was not respond to tantrums. The few times he'd flip out, throw things, lay on the floor, stomp his feet, and cry (sometimes all in quick succession) I'd just say "I see you're mad and that's okay. when you're done being mad I'll be in the living room and we can play with your blocks" then I'd calmly walk away. The point was not to invalidate his feelings by telling him he couldn't be mad, but to not engage.
My other guess is that she's on the verge of a verbal spurt and things will die down quickly once that happens (and she can communicate her wants better). It DOES get better =)