Lui for a man and a woman, vs Lui for man and Elle for woman

Question

In the following:ATTENTIONlui means either him OR her (depending on the context)But I've been given the following information which I am struggling to reconcile with:When you combine personal pronouns with prepositions such as avec (with), chez (at the home of), and pour (for), they change their form.Daniel habite près d’ici. On va chez lui ? Daniel lives close by. Shall we go to him?Sarah veut nous rejoindre. Il y a de la place pour elle? Sarah wants to join us. Do we have space for her? **why do we use elle in the above? isn't Sarah an indirect subject here? "Is there a space [for] Sarah**

Accepted Answer

Hi Ben, 
After 'chez', 'pour', 'avec' ( all prepositions) you will use a different kind of pronoun called 'stress' (sometimes also called 'disjunctive')  pronoun.           
The lesson you want is the following one -   
Moi/toi/lui/elle/soi/nous/vous/eux/elles - advanced usages (French Stress Pronouns) 
Bonne Continuation !