I was hardcore, I just never gave in to them when they were being unreasonable. Because the minute you give in, they will try it on again, and again, and it will get worse each time till they know you'll give in and give them what they want.
One of mine was a whingy, grumpy moaner at that age. But the grabbing things off his more mild-mannered older brother, I just never tolerated - ever. It was a "No, DS1 is playing with that. You can have it in a minute/when timer goes off." I just ignored the whining and screaming. Because they wear themselves out eventually. Or get bored of it.
Literally just carry on having fun with DS and ignoring the noise. Be stubborn, don't give in. Or have a laugh about it with DS.
Then when she CAN have a turn, you say "Oh, have you finished playing with that now, DS? Do you think DD can have a turn? Here, DD, DS is being very kind and such a lovely big brother to you and letting you have a go of the ball. THANKYOU, DS, you're such a nice to share with your sister!" Give him a big hug and a kiss and a smile. "DD, would you like to give DS a hug to say thankyou as well?"
I mean, really go to town over the whole praising of the right behaviour - with both of them. And basically just completely ignore the screaming. If she snatches, you are the parent, you just calmly take it back and firmly say "No, we don't snatch." And keep repeating that DS is still playing with it.
And you can do the same with DD when she has finished playing with something. Even if DS doesn't want it, perhaps you can quietly tell him separately that you are both going to teach DD how to share, and that he can help by pretending that he wants a go of something she's finished with it, when you ask. Big praises for her when she hands it over.
Always, always praise the behaviour you want (in an OTT way) and ignore the behaviour you don't want. Shouting gets everyone upset including you. And always explain the reason that something has to be done a certain way. And acknowledge that 2 year olds won't always accept that reason because their brains aren't developed enough yet, and they don't know how to cope with their frustrated feelings.
It's ok to acknowledge that they are feeling frustrated. "Ah, DD, yes, I know it's upsetting to have to wait for your turn. But you will have a turn eventually so that's ok."
You can do it. You're expecting her to behave with a reasonable mind but she doesn't HAVE a reasonable mind yet, she just has impulses and urges.
Also, if you really feel like you're going to flip and say something horrible you need to just leave the room (make sure they're safe) and go and make a cup of tea and put some music on or something.