Think of the quiet person who is always around but rarely noticed. The speaker describes her as kind, well liked, and accepted, yet people bump into her without apologizing and sometimes forget she is in the room. The repeated word "there," always in quotation marks, makes her seem less like a full person and more like a fixture, someone whose presence is taken for granted.
The speaker seems sympathetic and a little regretful. The question "But what is she feeling / Inside?" suggests that nobody bothers to ask, and that her calm look might be a disguise. The poem then warns that by the time you realize how cool she is, she may have moved on to better things. The ending offers a small hope: maybe she is still there, and you can finally see she always was. The mood is gentle, wistful, and quietly pleading, a reminder to notice people before they are gone.