Because she is a Capulet and her lineage makes her strong in the face of tragedy. She, through her actions, can send a message to both the Montagues and the Capulets that love, even in death conquers all.
Romeo goes to friar Lawrence about marrying Juliet
Friar Lawrence gives Juliet the potion to reunite Romeo and Juliet again from their parting. Juliet is forced to marry Paris and she does not want to. Therefore she goes to Friar Lawrence for help and he gives her the potion to get her life and love back
Juliet is much more free and open when in the presence of Friar Lawrence, which is not surprising seeing as how he is her confessor.
Juliet asks Friar Lawrence to marry her and Romeo at first, and later she asks for a way out of the marriage with Paris.
Romeo, Juliet, and Friar Lawrence are in Friar Lawrence's cell.
Friar Lawrence was a priest. He had no affiliation with either family.
Sleep Drug as Friar Lawrence is an expert of plants.
Romeo wants the Friar to marry him to Juliet.
The Nurse and Friar Lawrence
In the story Romeo and juliet, Friar Lawrence is a friend of Romeo's and Juliet's and helps them, gives them advice and also keeps their secrets.
Juliet refused to go.
He marries Romeo and Juliet.
Friar Lawrence was the priest in Romeo and Juliet
Friar Lawrence married Romeo and Juliet in his cell.
Friar Lawrence gave Juliet the poison in Romeo and Juliet.
He heard a noise of the guards and told Juliet to go with him, she refused not to go so friar lawrence went away.
I believe that Friar Lawrence made it himself, because he was talking about the flower that made up the potion. In the movie, it shows him making it and then giving it to Juliet.