Dancer Morleigh Steinberg, who will collaborate with her rock star husband on a new dance piece this month, told the press how Sian, now 13, was diagnosed with the life-threatening cancer a few years ago.
Steinberg said: "You're in shock then you just go into survival mode. The whole thing is hell but at the same time you stay positive and you really live. You live more because you don't take anything for granted."
News of their daughter's sudden illness first broke around the time U2 axed their 2006 Vertigo tour but the exact details were kept secret.
She was treated in Dublin and Los Angles and Morleigh said: "She's through it and she's fine."
The Edge, 49 - who's real name David Evans - has three other daughters from a previous marriage. The couple also have a son.