Conversation so far:
What was Sharon Cuneta doing in 1981?
On November 12, 1981, Viva Films released its first feature film, P.S. I Love You, starring Cuneta and Concepcion.
Was P.S. I Love You, the start of Sharon Cuneta career?
No, Cuneta first appeared on Philippine pop charts in 1978 with the Filipino pop culture hit Mr. DJ.
Did Mr. DJ do well?
The song became popular that gave her the moniker, DJ's Pet (which also became the title of her debut LP).

Question: What was the name of it?
Self-contained rewrite: What was the name of Sharon Cuneta's first career song?