There's something interesting I noticed when it comes to Barbie media. It's very rare for her voice actress to sing for her too. Another person is often brought in to sing for them. Kelly Sheridan and Diana Kaarina have had multiple singing voices between them during their time in the role that I can't list them all. For Erica Lindbeck's time as Barbie, her singing was done by professional singer Jordyn Kane (coincidentally, both of them would return on the same roles as Barbie's lookalike Princess Amelia in Barbie Princess Adventure). For America Young, she's replaced by another professional singer, Elli Moore. I don't know about Kate Higgins since she never voiced her in a movie and I don't know if she ever sang. I have wondered why this was the case given how the actresses can sing really well. Could it be the type of music? I've seen Kelly Sheridan sing as Starlight Glimmer in My Little Pony Friendship Is Magic, and she does really well. The same goes for Diana Kaarina as Blueberry Muffin in Strawberry Shortcake: Berry In The Big City, where she nails singing with a higher pitched voice. It seems like it's more for professional songs given how I think America Young does singing for Barbie when it's more casual stuff (like singing Christmas karaoke in a 2019 vlog) but she doesn't sing for the big musical numbers.