This is the 785th most frequent Spanish word.
sola
Alone.
In this sentence, 'sola' is used as an adjective describing a state of loneliness in the subject, which is feminine singular.
Ella se siente sola en su nuevo hogar.
She feels lonely in her new home.
Here, 'sola' describes the subject's (feminine singular) preference for being alone while performing the action.
Prefiero beber el café sola.
I prefer to drink coffee alone.
In this case, 'sola' attributes the chair, indicating it is solitary or isolated in the room.