Illegal Day Jobs are the easiest ones to explain away, concerning their pay rate. She's an illegal, black market, back alley, patch-up artist. She's got to pay off local gangs for "security" and "protection," has to pay some local hackers to rig up power and running water, has to pay off Knight Errant to look the other way, has to have some muscle on-hand to try and get payment from the two-bit razorboys and wannabe gillettes that pay her to give 'em new muscles, has to bribe at least one legitimate medical supply company to get parts in stock, and might even still be throwing nuyen hand over first at med school student loans.
Sure, maybe she's a full-on trained MD, and could be getting carted around town in a stretch limo Mercedes, doing cosmetic surgery for superstars and high roller executives...but she's not. She's a grimy, dirty, two-bit, illegal, street doc. Of course she's lucky to make ends meet and still bring home a couple bucks here and there!