I guess my point is, if there's no meeting of the minds, there's no contract. Make each party whole by offsetting her $60k hold by whatever she's paid in winnings.
I haven't read his response but I tend to agree with Cate that 50% of the profits and 100% of the loans is a pretty usurious loan rate.
I read a couple pages of the thread, and it sounds like Cate never made any profit while under the staking arrangement, so there's nothing to withhold.
Also, I think "50% of the profits, 100% of the loans" is a misrepresentation of the agreement (the backer says) they had. First, he's incurring a good bit of risk by bankrolling a poker player to move up in stakes. Also, he claims that after making a small amount of profit, the player share of profit goes up to 67%. Finally, the backer has the option (and sometimes exercises it) of ending the staking agreement, which in this case voids any makeup that the horse may owe.
I see benefit for both parties here: the backer can make good money off of a solid player, and the player gets bankroll protection and the ability to move up in stakes faster than they could if they were self-funded.
The obvious downside for the player is that if it doesn't work out, you're obligated to grind lower stakes to pay off your debt unless the backer releases you from the staking agreement (which does sometimes happen).
EDIT: Don't get me wrong, I'm not defending her or her actions (which do sound a bit on the unethical side), I'm just explaining what I think the upside of staking is for the player.