N7,000 a month? How do we enforce minimum wage in Nigeria?

I ran into a woman this week who earns N7,000 a month at restaurant in Surulere. She's required to resume by 8 in the morning and close at 8pm everyday, Monday to Saturday. She lives in Orile, which means she pays transport to get from her house to work every day. She told me that her boss gives her N200 every week as transport allowance. And she feels lucky!
I asked her why do you do this job, how can N7,000 help you survive in a month? And her reply was;

"N7,000 small? Many of the people wey I know no dey even earn reach N5,000 for one month. My small sister dey work for supermarket dey earn N4,000. Where I dey live people dey roam about they beg money wey dem go take buy food chop. Some people no dey even see N50 for one week. With my salary I go buy food stuff put for house for my pikin dem. I no dey too spend money for transport because I dey wake up early to trek reach (she mentioned the place - can't remember) from there I take bus reach Bode Thomas. And I dey collect N200 every week, so that one sef dey help."

I was amazed at how satisfied she was with earning that amount of money and surviving well on it, especially with two kids. But isn't the minimum wage in Nigeria supposed to be N18,000? There are millions of Nigerians who earn way less than that. Is there something that can be done about it? Is the Nigerian minimum wage applicable to private business owners or just government workers?