If I'm not mistaken, in order to qualify as a miracle for sainthood, it must take place AFTER the person's death.
The requirement is: two miracles (not "by" the saint, but by God through the saint's intercession.) Both after the person's death. One for "beatification" and the second for "canonization."
And the Church usually has skeptics, agnostics, etc. among those who are invesigating and evaluating the purported miracle, to confirm that it is truly inexplicable on a natural level, and not just a matter of wishful thinking.