"His daughter helps him."
Translation:Sa fille l'aide.
"lui" is the indirect form of the pronoun (à-il or à-elle).
since "aider quelqu'un" is directly transitive (no preposition needed), you use le or la - in this case l' because aide starts with a vowel.
Why doesnt ´Sa fille il aide' work? Im getting so frustrated with these pronouns..
"il" is only subject: il donne (he gives)
"le" is direct object: il le donne (he gives it/him)
"lui" is indirect object: il le lui donne (he gives it to him)
Verb "aider" is directly transitive, so you need the direct object form of "il" = le, which has to be elided (drop the vowel and replace it by an apostrophe) because "aide" starts with a vowel.