It's really hard, but when I am losing my calm I try (try!) to remember "they're not doing it TO me" it's really not about me, it's about what's going on in their tiny heads and hearts. My AD cannot manage strong emotions either, and goes from zero to rage in a milisecond. Spotting the early signs or triggers is hard work and is making me as hypervigilant as she is 
Some things that work for us -
get into water. Paddling pool, bath, big tub of water and bubbles on the floor, anything that LO can splash in. Cool water is even better, seems to have a sensory calming effect.
Visual timer - we have one of those things with bubbles that drip down. Something to watch for 2 minutes and create a pause before attempting to resolve whatever the problem is.
Playdough - almost as good as water if feelings spotted early, but need to encourage loads of hard squeezing with hands.
DVDs in episodes - we tend to use DVDs of things with fairly short episodes, to manage the screen time and help LO understand units of time a little. So one more "Little Princess" and then we're going to have lunch, for example. It's much easier than cbeebies which never ends...
Laughing - it's extremely hard but if you can be playful and get her laughing, you'll be able to distract out of the huge feelings a lot of the time. When I feel like screaming I sometimes stomp around the house gurning and singing the "I'm a silly monster" song (c) which has an amazing distraction effect as they beg me to stop!