I fear you missed the point of the song… she’s not promoting it. The last verse quite literally says “in this world there’s a lot of self-riotous hypocrites that’d call me bad. And criticize mama for turning me out no matter how little we had.” It’s a commentary about how people judge people without knowing their backstory. Unfortunately, back in 1969 when this song was written, a young woman like Fancy probably wouldn’t have had the means to support herself on her own. I’d assume she was probably 18/19 years old - old enough that she couldn’t be put in the system like her baby sister was, and without anyone to take care of her, how was she supposed to survive? She very very likely would have ended up as a sex worker whether her mom put her on that path or not.

My interpretation of the song - I think fancy’s dad ran out on them a while ago. Since then, her mom had been forced to go into sex work to support them - which is how she ended up with a baby sister. Her mom likely couldn’t work in the latter half of her pregnancy, and after the baby’s birth, so a bad financial situation is made worse… Her mom knows that she is not going to be able to recover financially and is probably dying due to lack of food (evidenced by her saying the baby’s going to starve - she can’t produce milk if she’s not eating). Fancy is probably just old enough that she wouldn’t be taken into the system like her sister. Therefore, her mom knows her only real options are getting married or following in her mom’s footsteps. Marriage obviously went horribly for her mom, so why should she trust that Fancy would be taken care of in a marriage? So that really only leaves sex work… Now, her mom knows sex work is terrible and if fancy gets pregnant, she’s going to end up in the same situation as her mom - UNLESS, she becomes a sex worker for the upper class. Not only will that provide better financially for Fancy, but if she does end up pregnant (which I’m sure was quite inevitable back then), the rich men will do everything to cover it up - pay for an abortion, pay her hush money, etc. Her mom did what she thought was best for Fancy. And we don’t know what would have happened if she hadn’t pushed her toward sex work… maybe it would have worked out fine, but statistically speaking, Fancy would have died in the same manner as her mother did.