if you have half expression of a particular genetic defect that runs in your family you have a great chance of giving full expression to a child if you are conceiving with a relative.
There is an interesting story about how it looks like Meghan Markle’s ancestor was a product of incest between two half siblings.
mental health issues may run in her family
Depends on whether it’s a recessive or dominant gene (and some other things too), but this was far enough back and distant enough that it is unlikely to have affected Ms. Presley.
Her lifestyle would have greatly affected her longevity though.