She just needs to keep practicing. At age two, it feels like "you are taking it", not "it's your turn". She's acting normal. But, repetition is the only way.
Maybe next time, give more time to each child. Like two times back and forth, then it's A's turn for two times.
I have kids in my daycare who will dominate every situation. It gets harder if you don't step in. When you aren't looking, the dominant child thinks up clever ways to keep or get a toy. I have a four year old that can manipulate almost every part of the day to her advantage. It's exhausting to keep up with it.
But, by you knowing she's strong, and caring about the feelings of others, this will make it so much easier for her to learn to take turns. She's still young now, but she will understand soon, and it won't be so hard.
Beware the traps I see parents falling into.... I have kids who will come over, and want a toy that someone is using. Then a parent will ask the other child "Can you share that with Bobby?"
Which means "I want you to give your toy to this other kid, because as you can clearly see the world revolves around him, and not you".
Or the parent who makes the older sibling give a toy to the younger sibling, so he doesn't cry. I (as the provider/teacher) don't really care if the younger sibling cries.... when the one who had it first is all done, then the other child can have it. The day is very long, there will be lots of chances to play with a toy.