Super System: I Open a Gourmet City in the Apocalypse

[No romance, management, supporting heroine's rise, cherished by all, world-building] Gu Xiyan, a billionaire heiress, transmigrates into a post-apocalyptic novel as a cannon-fodder supporting character. But she's not worried: she's bound to a System with a built-in pocket dimension. She thought the System would help her tear through scoundrels and zombies in spectacular fashion, but instead, from the start, it tells her to catch zombies and cook them. Gu Xiyan thinks this is utterly deranged, and she's the deranged one. Later, the System dangles a big promise: if she can open a food city in the apocalypse and collect enough happiness points from humanity, she can return to the real world and keep being a billionaire heiress. She agrees and starts working tirelessly to earn happiness points and upgrade her little food cart. Taking one solid step at a time, she fights monsters, levels up, builds a food city, and makes her way to the top! But the further things go, the more Gu Xiyan feels something is off. The food city is built, and more and more people are coming, but why does no one ever leave? Why are they treating her place like a shelter? That won't do. The prices have to double!