Learn Hardcore Spanish (Latin America): Ella termina la lección en la escuela.

In Spanish, subject pronouns (él, ella, usted, etc.) can often be left out because the verb form indicates the subject. However, using Ella can add clarity, emphasize the subject, or avoid confusion when the context is not completely clear.

Is termina the only verb I can use for "finishes" in this sentence?

You can also use acaba (from acabar) meaning "to finish," but termina is just as common. Both imply completing something. In Latin American Spanish, terminar and acabar are often interchangeable in this context.

Can I say "la clase" instead of "la lección"?

Yes, although la clase often refers to the overall class session, while la lección can focus on a specific lesson or topic. If you mean a particular lesson or portion of the class material, la lección is more precise.

Why do we use en to indicate the location here?

En generally means "in" or "at" when referring to a specific location in Spanish. Saying en la escuela indicates that the action (finishing the lesson) is taking place within or at the school.

How would I change the sentence if I'm referring to multiple lessons?

You would pluralize lección to lecciones, for example:
Ella termina las lecciones en la escuela.