The midwife is, to put it simply, Moll's hero. This woman seems to show up and help Moll whenever times are really tough. Unfortunately, though, we don't ever get to know her all that well. Nevertheless, let's take a moment to hash out the facts, so we might hazard a guess at what makes her so willing and able to come through in the clutch.
First she appears on the scene when Moll is single and pregnant with nowhere to go. Moll initially just dismisses the midwife with a dose of faint praise: "I found she was an eminent lady in her way" (644). But it soon becomes clear that this is a handy woman to have around. She really helps Moll – for a price, of course – until Moll can get through her tough time and get back out into the world, so to speak.
Meanwhile, we find out that the midwife has a few other careers too; she's not just a midwife, but a part-time abortionist, adoption arranger, and brothel madam. She, like Moll, is one resourceful lady. Moll also finds out later that the midwife was a criminal with the best of them and narrowly escaped a life sentence herself.
In this way, the midwife is a reflection of the different ways Moll's and her birth mother's lives could have gone. Since Moll's mom wasn't quite so lucky, the midwife winds up standing in as a mother figure. They're all criminals and all three women receive the same sentences once caught. Yet they all wind up on radically different paths. That's some serious food for thought for our Moll.
True to form, the midwife shows up again when Moll needs the kind of help that a man just can't provide. Now that Moll has grown older, and is therefore not the hot commodity she once was, she turns to the midwife for aid. The midwife becomes the one person Moll really seems to trust, and she repays that trust by helping Moll become a thief, and then selling the goods Moll steals on the black market. As weird as this sounds, the midwife has once again become like a real mother to Moll. While your typical mother figure doesn't usually help you become a thief, the midwife nevertheless provides help and (sometimes misguided) guidance when Moll needs it most.
In fact, Moll frequently refers to her with motherly titles and says at one point that "[her] governess acted a true mother to [her]" (1045). And the midwife clearly feels protective and loving toward her almost daughter. When Moll is convicted of stealing and finds herself in serious trouble, the midwife practically feels worse about it than Moll does: "My poor afflicted governess was now as much concerned as I, and a great deal more truly penitent, though she had no prospect of being brought to trial and sentence" (1048).
Ultimately, however loving or affectionate their relationship may be, when it comes to the midwife, it's all about how much she can help Moll. And in that sense, she is just like just about everyone else in the novel. After Moll is imprisoned in Newgate, the midwife does her dirty work, makes her financial arrangements, and ensures that Moll will be starting her new life in a far better way than most other convicts could ever dream of. Yet she gets left behind in England while Moll moves out to Virginia with the Lancashire husband. As much as she might love Moll and vice versa, the midwife's presence in Moll's life can't last forever. Do you think the pair reunite when Moll and Lancashire return to England?