Should I transfer to another store in the middle of being trained or after?

I work in a retail store and it’s a big company across Australia which means I can easily transfer to another store that’s the same company. So for example, I’m going to say I work at target (although I don’t) but the target I work at is about 20 minutes from where I live. There’s a closer target that’s only 10 minutes away that I’d like to transfer to:
1. Because it’s closer
2. The parking is free unlike at my place of work currently
3. I hate my manager at my current store

I’m a 16 year old girl and my manager is currently training me to run the store on weekends. I have a feeling she’s also training me to become an assistant manager because word on the street is she has cancer, unfortunately. So my guess is that the current assistant manager will become manager and then she’ll employ me as assistant manger once I finish high school.

Although I really can’t stand her as a a manager. She treats her employees like crap, swears at them, gives them one hour notice to take up a shift and then complains that no one is available, and she does not tolerate what she thinks are stupid questions, even if they’re not and she’s just not good at explaining what she wants people to do.

Anyway, two weekends ago I worked open - close on both Saturday & Sunday and that was when she started to train me. I really don’t know whether to move now, when she’s in the middle of training me, or after when she’s finished training me. Neither are good options because, not to brag, but there isn’t a single person who would be able to run the store (out of the teenagers). They’re all lazy or too shy or make too many mistakes, and that’s why she trusts me so much. So if I was leave now, she wouldn’t know who to train. But then I don’t want to leave after she’s trained me because that’s just rude and she would’ve wasted all of that time training me. Neither of the choices will have a good outcome and I’m really not sure what to do.
Should I transfer to another store in the middle of being trained or after?
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