Why was she the happiest person in the world?
The מדרש תנחומא (Parshas Shmini) says," We wouldn't find any man or woman as happy as אלישבע בת עמינדב. Her husband אהרן was the כהן גדול and a נביא. Her brother-in-law משה was מלך and a נביא. Her sons were סגני כהונה.
Her brother נחשן was the head of all the נשיאים. (The מדרש רבה adds, her grandson פנחס, was the משיח מלחמה)
This lasted only until she lost her two sons. (נדב ואביהו)
Therefore the פסוק in 'תהלים ע"ה ה says "אמרתי להוללים אל תהלו" and Shlomo in 'קהלת ב' ב said "לשחוק אמרתי מהולל"
It seems from this מדרש, that being related to and surrounded by great people makes a person happy.
vort for parshas shemini ,The key to happiness