100K is shorthand, and a nice big round number. Was Nicki's debt actually exactly 100K? No, of course not. Brent wanted 100K cause it's a large amount, Nicki owed 100K because it was a large amount; and NeonGhosts was just using large evocative numbers. Now if Brent had pushed Nicki to ask for exactly 79.5K, and later her debt was also that same strangely specific 79.5K? Yeah, you'd have more of a leg to stand on here.
But I don't think the actual numbers matter any more than the MC's actual wealth. They're meant to be evocative, a measure in relative change in each circumstance. When Nicki asks for 20K in help, and Brent on the phone wants 100K just because? That relative difference represents Brent's douche-baggery as measured in the orders of magnitude more money he wanted. When Nicki returns and tell of how Brent left her holding the bag, the increase in debt is meant to illustrate the relative increase in desperation and pressure on her. Neither of those numbers had to be exactly 100K, they just needed to be larger than 20K to illustrate the point; and again, 100K is a nice big round number that is both evocative and within the realm of possibility.
Also, if Nicki was really on the hook for 100K back in Ch1, that means nothing she said is true. The story about using 20K as collateral can't be true. Also, how did they even get into 100K in debt in the first place if they were in a paycheck-to-paycheck subsistence? What kind of secret collateral did they already have? Who was going to lend them that kind of money without collateral? Whereas Nicki's story in Ch3, the collateral was the 20K bailout, and the lenders were loan sharks. To assume Nicki is lying in Ch1, is to take on a massive truckload of other new assumptions that require new explanations. That's why merely from a simple probability standpoint, your take is far less probable; because it requires far more unexplained assumptions, it violates Occam's Razor.
