Stella is a fictional character in the cartoon series Hey Arnold!
Stella was a botanist/doctor who happened to be in San Lorenzo (as part of an archeology expedition, apparently) when Miles literally fell into her life. See the entry for Arnold's father for information on what happened next.
Stella's father was named Arnold - it is not exactly a coincidence, as that is who she named Arnold after.
Stella passed on her football-headedness to Arnold, who also got Miles' blonde hair.
Whether Arnold rescues them is left up to the audience since a planned movie that would show Arnold searching for his parents in a jungle was canceled after Craig Bartlett left Nickelodeon.
Stella was named after producer Antoinette Stella who also voiced her.