Learn Spanish (Spain): Ella me miró sorprendida.

In Spanish, it is very common to use an adjective that describes both the subject (ella) and the action (miró) simultaneously. This is called a predicative complement. While English naturally uses the adverbial phrase 'in surprise', Spanish prefers the adjective sorprendida to describe her state while she performed the action.

Does sorprendida have to agree with ella?

Yes. Even though it translates to 'in surprise' in English, sorprendida acts as an adjective here, so it must agree in gender and number with the noun it refers to. Because the subject is the feminine singular ella, the word becomes sorprendida. If a man had looked at you, it would be Él me miró sorprendido.

Could sorprendida refer to me instead of ella?

Grammatically, if the person speaking (me) is female, it is technically possible for the adjective to modify the object (meaning 'She looked at me, and I was surprised'). However, without extra context, a native speaker will automatically assume sorprendida modifies the subject, ella.

Why use the preterite miró here instead of the imperfect miraba?

The preterite miró implies a specific, completed action, such as a sudden glance or a distinct moment of looking. If you used the imperfect miraba, it would change the meaning to an ongoing action, translating more closely to 'She was looking at me in surprise' or 'She was staring at me'.