As far as I know, Sigma really wanted to collaborate with Ella, they wrote Changing together and she even recorded the vocals for the song. However, the last minute she changed her mind and decided to drop out because she was too afraid to become a typical "feature/hook girl". But yes, it was a very stupid decision and even Ella herself started regretting it once the song went #1.

OT: I hope this becomes a hit. The song is very good and Rita absolutely deserves to smash again.

It's going to be another Changing rehash