The first thing one would want to state in a death announcement is the name of the deceased and her relation to loved ones. For example, if we were writing a death announcement for Jane Smith, we might say, "Jane Smith, beloved daughter, mother of six, and wife of John Smith...." For Juliet, we will specifically want to point out that she was an only daughter and that she was the wife of the late Romeo Montague, only son of Lord Montague.
One will also want to include the date that she died. We know from the third scene in Act 1 that Juliet's birthday is in a little over two weeks because Nurse asks Juliet's mother when Lammastide is, which is the holiday that Juliet's birthday falls on. Lammastide was a holiday that celebrated the harvest and began around August 1st, hence we know that the play is taking place in the middle of July (Holidays, Festivals, and Celebrations of the World Dictionary, Fourth Edition). We also know that the play was written around the years 1595 or 1596. We also know that Romeo and Juliet's wedding night falls on a Monday, for Monday is the same day as Tybalt's death. Paris tells Capulet that the day is Monday when they make plans to marry Juliet to Paris on Thursday (III.iv. 18-20). As we see in the lines,
But, soft! what day is this?
Paris: Monday, my lord.
Capulet: Monday! ha, ha! Well, Wednesday is too soon. (III.iv.18-20)
We also know that the the potion Friar Laurence gives her wears off in 42 hours, as he states, "Thou shalt continue two and forty hours" (IV.i.106). Thus, Juliet would have married Romeo around Monday, July 16, 1595/1596 and would have been found in her state of faked death when Paris came for her on Thursday morning, around the 19th. If we count 42 hours beginning with the night she drank the potion, she would have woken up and died for real around Saturday the 21st.
One may also want to include a statement about how she died. In the case of Juliet it will sound very strange because first she faked her death and then slayed herself for real.
Finally, one will want to make up a location, day, and time for her funeral. Again, in Juliet's case this part will be unusual as well, because it will be her second funeral.