Spanish often leaves out subject pronouns when they are not needed.
Because trabaja already tells you the subject is he/she/you (formal), and because la chica is already named, adding ella would usually be unnecessary.
So La chica trabaja en la biblioteca sounds natural.
You could say Ella trabaja en la biblioteca, but only if the context already makes it clear who ella is, or if you want emphasis.
Chica usually means girl, but depending on context it can also mean young woman.
In everyday Latin American Spanish, chica can refer to:
The exact age or nuance depends on context.
No. Biblioteca means library, not bookstore.
This is a very common vocabulary trap for English speakers.
Even though library and librería look similar, librería does not mean library.
Yes, the most neutral word order is:
Spanish word order is often flexible, but changes in order can sound more marked or emphasize different parts.
This is possible, but it sounds more like you are emphasizing where she works.
For learners, the original order is the safest and most natural.
A simple pronunciation guide is:
The j in trabaja is pronounced like a strong, breathy h sound, not like the English j in job.
So it is tra-BA-ha, not tra-BA-ja in the English sense.
Also:
The ending -a often suggests a noun is feminine, and that is true for both chica and biblioteca.
So here:
But learners should remember that -a is only a common pattern, not a perfect rule. Some nouns ending in -a are masculine, such as el día or el problema.
That is why it is best to learn nouns together with their article: