I think the "collateral" makes that not so clear cut. I'm sure there must be BDSM clubs where everyone really is consenting, but this case is different. If someone says they were branded and became a sex slave of their own free will but the person who did it to them is holding blackmail material over their head, can you really say it was done of their own free will? Also I'm pretty sure there are laws against slavery even if the person in question "agrees" to be a slave. You can't legally sign away certain rights even if you choose to sign a contract saying so.
But, in the end, it seems like a lot of what they were convicted of were financial and procedural crimes (financial fraud, immigration fraud, identity theft, etc) - charges that aren't directly based on the creepy sexual "not against their will" stuff.
Yeah, I think she is guilty of illegal things for that, though to a lesser extent (e.g. it sounded like she quit before any of her slaves actually got branded, and maybe she can claim that she never intended to actually use the blackmail material and stupidly didn't believe anyone above her would either - when she asked for her collateral back it sure seemed like she didn't get what the point of it was).
But, it's not uncommon for prosecutors to go after the "big fish" and not prosecute the ones who did lower level crimes and are willing to cooperate as witnesses. This reminds me a lot of prosecuting a mob boss (who carefully avoided getting his hands dirty where anyone could see) and the few top kingpins - the DA is going to be perfectly happy not to charge some low level flunky who came to them with evidence, even if they are also technically guilty of crimes. We saw Sarah asking everyone to submit evidence of illegal activity that they witnessed *or took part in*, and none of them seemed to be very worried they'd be prosecuted. They know they're needed as witnesses against the big fish.