Cassandra was hit and died at the scene. Her friend ran off without being hurt.
Police said they have no suspects and no arrests have been made.
Friends and family members, including the victim's mother, spent several hours Wednesday grieving near a makeshift memorial.
"She was a really good girl, but there's just too many gang members that don't get or care who they shoot or what happens to someone. They don't care; they don't have a conscience," said the victim's mother Francis Jacobo.
"She was very generous with other people. A lot of people cared for her and there's a lot of us in shock," said Lorie Jacobo, Cassandra's sister.
Police said they need the public's help in solving the murder. Anyone with information about the shooting was urged to call Pomona police detectives at (909) 620-2095, or the tip line, (909) 620-2085.
The Associated Press contributed to this report.