"Both girls were gone in one year. So we moved over to be closer to them. That made it less hard," she explained.
Ali and Bono have four children -- Jordan (24), actress Eve (22), Elijah (12) and John (10).
The couple's two daughters both upped sticks and moved to the US when they started college.
Jordan (24) went to prestigious Columbia in upstate New York, while Eve is currently studying acting at New York University in Manhattan.
"Jordan's just graduated from Columbia. She was doing politics and French which is very different from Eve," Ali said.
Initially both Ali and Bono had their reservations about their youngest daughter going into the world of acting.
Earlier this month, Eve said that her mum and dad were "terrified" with her decision.
"It didn't go over so well with my dad that I wanted to go into the world of acting," she said.
"I've been acting since I was 15 and my parents were just terrified. I think because they've been around and know what Hollywood is, especially for a woman.
"I think when I got into acting college they got into it and they knew I was going to take it seriously."
But Ali says she's delighted that her daughter is doing something that she's passionate about.
"I'm just happy for her and I'm happy that she's found something that she really loves.
"It's a tough career choice but she loves it and she seems to be doing quite well at it. I hope it continues to be successful."
And Eve has already got some impressive roles.
She starred in This Must Be The Place with Oscar winner Sean Penn, and she's just finished a new comedy with Muriel's Wedding star Toni Colette.
"She's only got a small part in that new movie. She's just finished another one but she's working away, doing all her studying for college," Ali said.
And Ali admits seeing her daughter on screen seems totally natural.
"I don't find it weird at all seeing Eve on the big screen. I'm well used to it with my husband," she laughed.
The star was speaking at the launch of Secret Art, a celebrity art exhibition in the Royal Hibernian Academy.
Celebrities including Colin Farrell, Grainne Seoige, Mel C and REM's Micheal Stipe have all donated original art work to the exhibition, which opens on November 21.
The celebs were given the raw materials to complete a masterpiece and were allowed to paint whatever they wanted. There was one condition, however, none of them could identify or sign their art work.
The pieces will be available for purchase on the November 21 with all proceeds going to Chernobyl Children's International.