Wow!
And before you ask, I'm not laughing at you.
I really don't think you "get" it at all. Sexism? Where? Who is being sexist to whom? Why are you so fixated on money? The Witch book harken back to a time when people used their skills in exchange for other people's skills. It's not about money. As far as I'm aware, Tiffany never sells her cheeses. And the money that Nanny made from the apparently only book she wrote all got spent in Maskerade. Nanny saw very little of it.
And why shouldn't teenagers read about incest, wife beating etc.? As Terry has said himself, there is nothing in these crimes that a teenager couldn't read in more detail about in the daily newspaper.
I do not understand your reference to "To Kill a Mockingbird" at all.
Why do young witches work so hard? They are doing an apprenticeship and are, apparently happy to do so. Nobody is making them do these things. They are learning about life and death and all things in between. Yes, they are nurses, healers, morticians, judges, teachers and social workers and a whole lot more. They are respected members of the society they live in and yes, they could probably use magic, but why would they do that when they don't have to?
Being a witch is very different to being a wizard. Terry dealt with the differences as far back as Equal Rites. Wizards use magic to command nature. Witches use nature in all its forms to produce a much subtler and longer lasting magic.
Finally, it was not so uncommon even in the 20th century for young girls and boys to be earning their keep at a very early age. I've known people in my own lifetime who were sent into "service" as young girls of the age of 12. Likewise getting married at a young age. This still goes on in many parts of the world.
It's not sexist - it's the reality of life. That's what Terry writes about and that is why I read his books.