The star – who plays Donna – was of course talking about Amanda Seyfried, who plays her on-screen daughter Sophie.
“I think Amanda brings something to this particular incarnation of Mamma Mia that’s very special,” she said.
“She’s the heartbeat of the film. Her emotion carries the whole story forward and she really moved me.
“I think she’s magic.”
Streep added: “Plus, she’s got a cracking voice and she gets to use it more in this one.”
The acting legend doesn’t appear in the sequel as much as she did in the 2008 original, but still makes a big impact.
Lily James plays the younger incarnation of Donna here, and Streep has been similarly complementary about her.
“I had no idea Lily James had the singing chops,” she said.
“Some people sing from the bottom of their feet, right up. She shakes the rafters, she’s amazing.
“Lily has a great energy. And her spirit is what young Donna was.”
Judy Craymer, the creator of the Mamma Mia machine, has explained Streep’s diminished screen-time in the sequel.
“I think for her, it was a matter of what and how, and we also did chat occasionally about it. It was a matter of the right script,” she told The Hollywood Reporter.
“Also, Meryl likes to conquer new things, and she had played Donna Sheridan and been singing nine or so ABBA songs in the first movie. I think she felt that she liked the idea of leaving this to the younger ones and she wanted to be involved, but she wasn’t gonna take on such a big role.”
Mamma Mia: Here We Go Again is out now.