The debt...

How much is the debt?

First victim : Zoro

She voluntarily lent Zoro some money.

Episode 48

And then use it against him.

Episode 66

Ouch! That pride

Zoro is so ungentleman...

Chapter 111

The debt also had been brought up once in episode 102 (filler). 

The debt is a taboo

*****

Second  victim : Luffy

Episode 88

That naive Luffy....

28,800 -> 100,00... that's way too unreasonable

Chapter 150

*****

Third victim : Sanji

Episode 588

Nami inside Franky

Sanji inside Nami 

And Chopper inside Sanji

Chapter 663

I didn't know that she kept the record in a notepad...

P/S : That debt thing no longer been brought up... Did they pay her back?