There aren't very many songs about the girl's name Sandra that come to mind, other than Sandra Dee from the famous 1978 musical movie Grease. There's also the reprise at the end of the movie, called Goodbye to Sandra Dee.
Sandra by Barry Manilow (also covered by Dusty Springfield)
Although the name 'Sandra' isn't actually mentioned in the lyrics, this song is about a housewife and mother called Sandra, as the title suggests.
Golly Sanrda by Eisley
The song begins "Golly Sandra/You've grown up really crazy" and seems to be about the relationship between a parent and child, sung from the perspective of the parent.
Mambo Number 5 by Lou Bega
This song isn't really about someone called Sandra, but it does mention a girl with that name in the line "A little bit of Sandra in the sun."
You can look up and listen to all of these songs on Youtube. Hope this has helped!