@MisterD The fact that a non-resident independent contractor who provides services to CA businesses must pay CA taxes on that income is a very recent development, and is due to two court decisions made this year (2019) - the most recent of which was a month ago. Thus it's very possible that you may run across older answers on this board that were correct at the time, but are correct no longer. You can read the details of those court decisions here: https://www.coblentzlaw.com/california-office-of-tax-appeals-gives-precedential-authority-to-bindley...
Second, since she is a MI resident, her CA income also must be included on her MI tax return (as well as on a CA non-resident return) - but she'll be able to take a credit on her MI return for the taxes paid to CA, so her CA income in effect won't be double-taxed. MI can tax its residents on all their income, regardless of where it was earned.
Finally, your statement that no one should put trust in any advice on this discussion board is unfair. Many of the volunteer users on this board have years of experience answering tax questions, and the advice they give is both accurate and excellent.
**Answers are correct to the best of my ability but do not constitute tax or legal advice.
