Likewise, The Last Kingdom TV show covers these characters probably even more - Æthelflæd is in all 5 seasons [1] (although season 5 isn't out yet), and there's a lot of focus on Mercia.
Unfortunately that show has some odd changes to history done for the purpose of entertainment. Particularly on her character, and the history of Mercia and its relationships.
[1] https://the-last-kingdom.fandom.com/wiki/%C3%86thelfl%C3%A6d
Edit: Should have hit refresh rather than browse tabs opened a while ago...err, I agree with dave333