Why would she mention a "basement" and a "penthouse?" What do they symbolize?

Native speaker’s answer
Rebecca
Here, "basement" and "penthouse" are part of a metaphor. Generally, a "basement" is one of the worst parts of a house or place, and the "penthouse" is the best part. So here she's saying that she wants to be placed in the best spot in someone's heart. She wants to be the first priority in a relationship, in the "penthouse," rather than thought of last in the "basement." Ex: I hate going into the basement. It's so scary. Ex: I would love to live in a penthouse one day! Ex: I feel like she's forgotten about me and left me in the basement. => metaphorically Ex: He treats me like I'm the penthouse of his heart. => metaphorically