There is no law on who has the right to be at the Oscars. From famous celebrities to nobodies, anyone who can get a ticket can attemd and Marie Kondo is no exception. It is rumored that there may have been two possible reasons for her appearance. One was that she was invited there to show that they are not racial nor are the chavanistic. By invitiing a Chinese woman, they tackled both.
Another theory is that it was a joke of sorts why she was invited there. The fact that there are always messes to be cleaned up at the Oscars went right along with inviting the most notorious mess organizer and cleaner ever to the occasion. But, yes. She had a right to be there because if not, many others would not have that right either.
Marie Kondo may not have acted in any film but I am sure the Academy reserve the right to invite any guest they like, and you cannot deny the stardom of someone who has changed people's everyday lives, according to their own report, and this means the lives of stars as well as those who never caused a ripple of attention anywhere.
Marie Kondo was invited to the event by "Access," an on-air entertainment news show that also helped her find her delightful pink dress.