Are you really sure Heroine was recorder before Sineads first album, cause
it I vaguely remember that it was
done because of doc. about a ghetto in Dublin [flats], where was a lot
of poverty, bad social/economical situation, lot of drug using...etc.
and did the members of U2 knew Sinead before she even made a record?
I'm not familiar with this Dublin documentary (and I don't see anything about it on her IMDB page), but I wouldn't be at all surprised.
Quoth Wikipedia, FWIW:
Musical career
O'Connor's time as singer for Ton Ton Macoute brought her to the attention of the music industry, and she was eventually signed by Ensign Records. She also acquired an experienced manager, Fachtna O'Ceallaigh, former head of U2's Mother Records. Soon after she was signed she embarked on her first major project, providing the vocals for the song "Heroine", which she cowrote with U2's guitarist The Edge for the soundtrack to the film Captive. While she was building bridges she was also burning them. O'Ceallaigh, who had been fired by U2 for complaining about them in an interview, was outspoken with his comments about music and politics, and O'Connor began to adopt the same habits; she made controversial comments about the IRA and even directing negative remarks towards U2, who nonetheless admired her music.
In other words, U2 knew her before her first record came out because she was active in Dublin's musical scene.
Oh, and "Heroine" is not about the drug, hence the "e".