Very common, not unusual at all.I honestly have no idea what to do with her at this point. I realize she is young but I have a hard time believing most kids her age have such inconsistent styles/mechanics from week to week.
Here is where I would start.
Get in front of a mirror and take your stride, and hold a 45 degree inward coil (hip and shoulder) until landing. Do this for a few days until you get the hang of it.
You don't need to try to 'sit' or 'set' or 'crimp' your hip, or pick your front hip up in the air, or have a certain leg kick, just rotate your torso - it's simple.
Keep the back heel on the ground, and stride with the back leg until it's almost fully extended.
Then add in, pulling the back elbow like a 'bow'.
That's it. Don't need to buy a bat, learn to slap, pay instructors, or join a club. She can learn the basics in a few days.