Eeesh. If I wanted to drive, I would use an online course to get past the initial bit and earn my learner's permit, then get a private driving tutor to handle the driving hours bit. Or at least I think that's how it works, or can work.
I don't think going to a driving school is necessary, at all. I had this online course with an annoying robot mascot... well, it worked. And then I opted not to continue working towards a driver's license. It's an unusual decision, but I don't think I could trust myself to do it safely at my current age.
So, here's my dubious life advice.
Find a junky old car for sale. Needs to be real cheap. Talk to your mom about buying it together. She'll pay the deposit(there generally is one, right?) and you'll work a part-time job or find some way of earning money to pay off the debt. Meanwhile, you have a car that isn't your mother's to practice with, which she should be okay with. She would still have to supervise(unless you get a tutor), but she wouldn't have to worry about her own car getting wrecked.
Find the evidence about the insurance discount not being cumulative, then present it to her when she's in a good mood and most likely to respond well. Use multiple, up-to-date sources to counter the objections of "this one's wrong, has to be" and "out of date", and preferably, get a government source, because it's something far less likely to be argued with.
Note that my knowledge of this subject may be incomplete or downright false, so be careful to do your own checks if you do act on my advice. Cheers.