This is very surprising news since my impression is that her bad singing onscreen in My Best Friend's Wedding and The Holiday are a reflection of her true inability to sing well. (She was dubbed in The Mask.) And she has old quotes on the internet that she doesn't think she has what it takes to star in a musical.
I'll keep my fingers crossed, but I hope she's not like Pierce Brosnan in Mamma Mia!
"What was the name of that cheese that I like?"
"you can't run away forever...but there's nothing wrong with getting a good head start"
"well I hope and I pray, that maybe someday, you'll walk in the room with my heart"