Why was Saint Martha canonized?

Martha was a close friend and disciple of Our Lord. She sometimes hosted him and his apostles at her home in Bethany. She eventually died a natural death and was not a martyr. She was never officially canonized as a saint as she was precongregational - before a formal proceedure for canonization existed. Basically, she was declared a saint by popular acclamation.
St. Martha was declared a saint before the official canonization
process was instituted in the 12th century. She would have been declared a
saint to the bishop by those who knew her best and were familiar with his
life and merits. The local bishop would them make the decision. Today
only the pope can declare saints after years of study by the Sacred
Congregation for the Causes of Saints in the Vatican. The church does not
create saints. Only God can do that. The Church "screens" candidates for
sainthood to determine if they had a life worthy of emulating. In other
words, do they make good role models. Also, the Church has to be assured
that the person is actually in Heaven. That is the reason that today a
number of miracles must be verified before a person can be declared a
saint.