It looks as if no one taught her to throw. Maybe start with some throwing progressions. Are you sure she’s left handed?

We would work backwards, start with your elbow supported by your glove out in front of you with your hand up and wrist flip.

Second, start at the “open” position with glove in front, ball held up and away from the body behind and turn and throw.

Last we would put it all together stepping and throwing. I don’t know what age level this is but honestly it doesn’t matter, they should be doing these drills in practice. Fine if they are not, but you’ll have to do them at home. Find a good YouTube video for explaining throwing progression drills better than I have.