Her father was a concert pianist and very wealthy businessman who invested John’s and her money shrewdly.
Story I always heard was Yoko came from a long time banking family. IIRC J Lennon left her a hundred million or so..... There were millions in royalties coming in each year.
Plus she had excellent advisers to help her grow what she got. I cannot stand the evil bitch but I admit she is good with money.
She was too unfeminine, hairy and ugly to find a good marriage partner in Japan. She was smart to go looking in the USA and Europe via her art pursuits which were as inane as her alleged music