How did St. Cecila become a saint?

Cecilia was not canonized. She was proclaimed a saint by early Christians because of her martyrdom. At first, the Roman authorities tried to kill her by suffocation but after 3 days in a hot, steamy sauna she was still alive. Next they tried to behead her but, after three tries, she was mortally wounded but still alive. During the next three days, while she lay dying, she arranged to have all her wealth distributed to the poor.

The canonization process did not come into existence until the 12th century. In the primitive Church, martyrs were immediately recognized as witnessing to the perfection of Christian life on earth, having shown the ultimate proof of their love for Christ by the offering of their lives. By the sacrifice of their lives for Christ, they attained Heaven in eternal glory and were indissolubly united to the Lord, the Head of the Mystical Body.