How did Donna from Mamma Mia die?

In 2008 a movie called Mamma Mia was released. And it featured the cast singing the songs by Swedish pop group ABBA. It starred Amanda Seyfried as Sophie Sheridan, Dominic Cooper as her lover Sky, Colin Firth as Harry Bright, Pierce Brosnan and Sam Carmichael, Stellan Skarsgard as Bill Anderson and Meryl Streep as Sophie's mother Donna. Christine Baranski and Julie Walters play Donna's friends Tanya and Rosie who help make up her girl group called Donna and the dynamos. And it's revealed that Sam, Bill and Harry are Donna's 3 former love interests and one of them may or may not be Sophie's father. The movie follows Sophie getting married to Sky and she wants one either Sam, Bill or Harry to give her away at the wedding. Then 10 years later a sequel was released called Mamma Mia Here We Go Again. And like the first movie, the cast sings songs by ABBA. However this time the movie centres around the reopening of Donna's hotel from the first film. And it's revealed that Donna died in between the events of the 2008 and 2018 movie. Lily James plays Donna in the past whereas the past version of Tanya is played by Jessica Keenan Wynn and past Rosie is played by Alexa Davies. Luckily Christine Baranski and Julie Walters still play present day Tanya and Rosie. However the only time Meryl Streep appears is through portraits, at the church and during the super trooper scene at the end. So with all that out of the way. What caused her to die in between the events of the first and second movies

How did Donna from Mamma Mia die?
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