Simply, she needs to come out to a practice.
There are a few things you can do to prepare your dog. The best is to play with her with a lunge whip.
This is a buggy whip, (horse tack shop), strong fishing pole, etc. Approximately 6' long, with 6' of strong cord tied to it. And on the very end, tie a white plastic bag (tall kitchen sacks)
I'm not a big fan of using fur, as some lunge whips are sold.
Now the fun, use the whip to move the bag about on the ground. It's a game, catch it. It's important for you to challenge her to catch it. Move it about her feet. After a while it will be challenge to keep it away form her. You do need to let her succeed, if she can not catch it, she’ll give up. Always end the game after 10 minutes or less, leaving her wanting more.
Do not play when there are distractions, or it’s to hot. We add this later after she has strong desire to rip up those plastic bags.
One done, you probly be cleaning up pieces of plastic.
The true test, is when you can come home and leave a plastic grocery bag on the floor with ice cream, and she attacks the bag, and leaves the ice cream alone.