How common is sudden adult death in a 23yo female?

Quite rare: Sudden death is rare in young people, about 450 in 2.5 million people. Nontraumatic, sudden deaths usually male (71%). Cardiac accounted for 56% of causes. Most common cardiac cause of sudden death was arrhythmia . Other less common cardiac causes were acute myocardial infarction.

Very rare: it is a very rare occurrence - so rare sudden deaths of young people often are covered in the news