object pronouns

Question

In the sentence : Tu parles à ta soeur. Tu lui parles. - why do we use ‘tu LUI parles’? Should not we agree the pronom with ‘la sœur ‘ (féminin) and say ‘ Tu elle parles’?

Accepted Answer

The indirect object pronoun of third person feminine singular is lui. Elle is the third person personal pronoun used for the subject of a sentence, not the indirect object. You can recognize the indirect object easily, because it frequently follows a prepositions such as à in this case.
Tu as parlé à Anne? -- Oui, je lui ai parlé hier.
https://french.kwiziq.com/revision/grammar/when-to-use-lui-and-leur-to-replace-specific-people-with-him-her-and-them-indirect-object-pronouns