The coach throws the ball to the goalkeeper, and that is the signal to A and B, who start running along the sideline.
The goalkeeper throws the ball to A.
A passes to B and runs behind B, who again flicks the ball to A.
A shoots.
After the shot A pick up the ball and runs to the coach without getting in the way of the next running players, and place the ball beside him.
Then she runs behind B's line, while B runs behind A's line
A new ball is thrown to the goalkeeper and so on....
Remember to switch goalkeepers.

VARIATION:
The goalkeeper decides to whom she will pass the ball.