I still don't understand why, if her soda addiction is solely because she needs the caffeine, she doesn't make sweet tea. Black tea contains plenty of caffeine, and when you add as much sugar as Southerners tend to do, you can buy a big box of the cheapest tea bags and a bag of sugar and have many weeks' worth of caffeinated sugarwater at a very low cost.
Alternately, if it's just about the need for caffeine, she could buy pure caffeine in 100 or 200mg capsule form, which is the cheapest way to support a caffeine addiction. It's cheap enough that she could easily afford to stack it with 1-2x L-theanine to keep any jitters at bay.
Bit it's not that Polissa can't; it's that Polissa won't.
A lot of white Americans (especially at lower socioeconomic levels, and who don't still have ties to a specific ethnic culture) don't know how to season bland staples like rice and beans to make them not just palatable, but delicious. Really; they don't. So I have no reason to believe Polissa has any clue about how to use herbs and spices as anything more than kitchen decor.
So when your palate is already blunted by a steady bombardment of extremely sugary and salty convenience foods, and you haven't the first clue how to season anything beyond throwing in tiny amounts of long-expired dollar-store herbs and spices, or dumping a packet of "taco" seasoning in with a pound of ground beef, beans and rice are going to be bland and taste like poverty, rather than something delicious and satisfying. Moros y Cristianos, or Louisiana staple red beans and rice, or lentils or chickpeas in a curry, are all delicious, and don't taste like "poverty food," despite being invented by poor people, but they all require far more seasoning than somebody like Polissa can ever imagine using.