She isn't mean - she's terrified. She's just three weeks old. Has she even had her first meal yet? She's a baby, you're a huge heat emitting predator in her eyes. She gets put into a bag, which she finally escapes, the predator picks her up and she uses the only means that her tiny body has to defend herself, which is to strike out to try to ward off this huge predator.

Give the baby time to settle into a nice cozy small enclosure (I'm using six quart tubs for my hatchlings) with a tight hide with no touching for a week, offer her a hopper mouse, if she eats, you can work on short, positive interactions with her (15 minutes a day). If she doesn't eat, leave her alone another week and repeat until she feeds for you.

Understand the snake, and where she's coming from. She's not mean, she's frightened.