I've always pronounced ð as an eth- or a th- and the æ as a regular -a- (like cat), so
Æðelflæd would be pronounced something like ath-el-fled or ath-el-flad. However, the æ has always been confusing for me- apparently in Old English it was pronounced like ash which later became -a- in Middle English, I don't know why. But apparently it is commonly said like cat or bat. I posted some links below that explains some of it- the last two links show how the ð and the æ are pronounced.
https://oldenglish.info/advpronunciationguide.htmlhttps://thegriffon.wordpress.com/name-list/ae/aethelflaed/https://www.grammarphobia.com/blog/2011/05/ae-digraph-ligature.htmlhttps://www.youtube.com/watch?v=4kwDHWHZJ8chttps://mythatsenglish.blogspot.com/2011/12/pronunciation-vs.htmlhttps://www.englishlanguageclub.co.uk/th-sound/https://www.englishlanguageclub.co.uk/ae-sound/
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