The Mint is an area near London that Moll moves to when her marriage to the linen-draper falls apart. Broke, desperate, and alone, she must hide from his creditors and figure out a way to get her hands on some cash. The Mint seems like as good a place as any to do those things. And for a little while, it's a safe place to be.
Of course she's only there for a brief period of time, because her need for dough sends her back out into the English countryside in search of a man with deep pockets. But despite the briefness of her visit there, it foreshadows Moll's future as an all-out criminal. The Mint, after all, was "a district outside the London city limits in which debtors could have refuge from their creditors […] so called because coins were stamped there in the sixteenth century. The Mint became known as a place frequented by criminals; the Mint was abolished as a debtors' sanctuary in 1723, the year after Moll Flanders was published". This little tidbit tells us that Moll is already on the path to becoming a part of London's underworld. It's just a matter of time.