My guess is daddy is unknown but probably in prison, dead or just a hood rat that knocks up girls one after the next. Mom is a drug addict/hooker, and/or barely a teen herself. Not uncommon for the offspring in these situations to get dumped off on grandma to raise, many of these grandmas still in their 30s.
But, that is absolutely the proper solution since grandma in these situations typically refused to forgo staying home and parenting her child in order to buy nice stuff and develop and impressive resume. If you are there disciplining and nurturing your child they generally turn out well.
Guess what?
If you screw something up because you refuse to do what you were supposed to do then you often get to do it over until you do it right.
No sympathy for Grandma.