Squeeze's (Jools' first succesful band) first single was released in July 1977.
Wuthering Heights was released the following January.
However her record company had been nurturing her for at least 3 years as they realised what a talent she was, and didn't want to rush and therefore spoil her.
Incidentally, She wrote The Man With The Child In His Eyes when she was 13.

That's not to say they hadn't met before, and you don't have to be famous to "discover" someone if you have the right contacts.

I reckon by the time she was old enough to go to the pub legally, her career was well under way anyway.