At what point does this come close to breaking antislavery laws? Where do you cross the line into indentured servitude? At 51% of salary, 100%, where?
If anything, this is a decent-sized loan, with a very safe, variable repayment amount that is defined to always be a small amount of her income, and the collateral is a company that may or may not succeed. More than that, the investor only even takes the company if she's dishonest. There's almost no downside for her here.
If you want to be concerned for someone, I'd be concerned about the investor.
To your earlier question about 51% or 100% of her salary, if an investor loans me $500,000 at 0% interest to pay back in 10 years, and I only make $50,000/yr, that would suck, but I'm not becoming a slave to that investor. I can't afford to pay that back, so I'm going to default on my loan. There's a huge difference between that and literally being owned by someone.
Thank goodness sewage and water are public utilities, rather than corporate entities striving to make greater profits.
There are some weird nonlinearities to this problem. For example, if 1% of a typical top-25 college STEM major's (lifetime) income is worth $50,000, then my estimation is that 10 percent is actually worth $1-2 million (20 to 40 times more). Why? Because, with that money and the cushion, he'll be able to take more risks and have a better career. But then at 50-100%, you get a Laffer-curve effect. So the value of N-percent of someone's income is:
(a) faster-than-linearly increasing for a while (career benefits) until it peaks and plummets (Laffer effect).
(b) not necessarily well-defined, because the infusion of capital has career-building effects that mean it might be better to give more money (for equivalent percentage).