Board Thread:Questions and Answers/@comment-24084046-20151011075435/@comment-26871105-20160510154938

Joseph talked with Lisa Lisa after finding out about Dio's re-surfacing, which would mean Lisa Lisa was about in her mid to late 90s during that time. And given that Joseph traveled to Japan shortly afterwards without ever showing concerns throughout the entire Part 3 on her  wellbeing, I say it can be assumed that it's one of the 2 scenarios:

Either she'd already passed away before the start of Part 3, or that she was in too good of a healthy state due to her hamon mastery Joseph felt no need to worry about her.