Aside from being totally delicious, food helps us know where we are. Shrimp and grits? You're in the American south. Philly cheesesteak? You're in Philadelphia. (At least, you'd better be.)
Doukona, pepperpot, and dasheen what-are-dasheen-chips? You're chowing down in the West Indies. Mom teaches Girl how to make all of these and even how and where to plant the vegetables.
Since food is the main way that we learn about the culture in the text, it becomes a symbol for culture itself. By passing down this wisdom and knowledge (that girl probably can't learn in school or from books), Mom is passing on her culture and making sure that it continues to survive.
Mom could have told Girl how to prepare for holidays or play Antiguan music (except benna, of course) but she chose to teach her about food. And who traditionally does the cooking? Mom. Sure, there might have been some West Indian dads cooking dinner in the 1950s, but we’re going to guess not many. There's a reason we think of mama’s home cooking.
So, food is a part of culture that, unlike holidays and other things, is prepared, eaten, and shared every single day. But it's also something that's tied to being female and a mother. And what’s this whole thing about? Teaching Girl how to be a woman and a mother. (But not a slutty one.)