On Frida's 1996 album Djupa Andetag, Marie sings a duet with Frida called "Alla Mina Basta Ar". Prior to that, the two of them collaborated on other projects, such as the Artister för Miljö gala in 1992.
I feel like I should actually go and listen to some of Marie Fredrikkson and Roxette's work, so I hope to spend today doing that.
Rest in peace, Marie. <3