Uh... She changed the season to Spring. She gave birth to Melinoe and Macaria. Melinoe is the goddess of offerings made to the deceased. Macaria is the goddess of blessed death. Both of their father's are Hades. She also helped keep the Underworld organized and all. In some ways you can see that as helping humans. :)
Persephone freed him from the chest that Aphrodite had put him in and given to her.
Demeter found Persephone with the help of Hecate and Helios.
Zeus is Persephone's father. He promised her to Hades to be his wife. However, he neglected to inform Persephone or Demeter of this promise.
Persephone did not have a favorite: as all people die whatever their city.
Persephone is a very compassionate Goddess, she does not do harm to people. The only reason she ever would is if they crossed her in a negative manner.
Persephone does not have a personal city: the people of all cites die and come to the Underworld where she is Queen.
It is indisputable, as Persephone was a ancient Greek goddess who was worshiped in many location and by many people.
To help rule the Underworld and create Springtime.
All people who die go to the Underworld, so Persephone need not have a favorite city.
All people die no matter the city, so no Persephone was not a patron goddess of any place or city.
People read about her tale and liked it.
By prayer and sacrifice and offerings.