I figured she had already worked with him! She's been on tour up until now so between her schedule and his own projects with other artists, they probably haven't had the time to get together.
Wait, he produced one of the best tracks on BTW 'Scheisse'?! I had no idea that was his doing. Lord I'm so glad to hear they're working together again!
She would be a fool not to include their (I say this because his work without her doesn't compare) songs. There isn't really one song he worked on that I don't love; his BTW songs are the best on the album