It's infallibly defined that she was taken up to heaven, body and soul.
However, the decree doesn't say she died, nor does it say she didn't die. It says "at the close of her earthly life". This was deliberate, to avoid making any dogmatic statement on the question of whether she died or not.
SD just brought up a similar statement. Kind of funny though, many Catholics I have met say that the pronouncement was that Mary was taken to heaven before death. Have to look it up now for our annual after Thanksgiving discussion.