In Hamlet in what way are we prepared for the tragedy described by the Queen in relation to Ophelia's death?
There are several ways in which we could have been prepared for the news of Ophelia's death. The first works only if you have read a lot of Shakespeare; typically, Shakespearian tragedies play out with most of the key characters dying at some point. Ophelia was definitely a key player, and was due for death simply because she existed in Shakespeare's tragedy. It's a rather basic reason, but, one that can be used as a fairly good prediction in Shakespeare's tragedies.
Another way the reader was prepared was through the simple facts surrounding Ophelia's life at that point. She was forced to reject her boyfriend (Hamlet), her brother left her to go on journeys of self-discovery, and her father was murdered by her ex-boyfriend. She was totally alone, betrayed, and manipulated. That's enough to drive anyone insane, or, to consider suicide. We are also prepared by her nonsensical ramblings in the scenes before her death; it becomes obvious that she was insane, and had lost any sense of her bearings or reason. She was also naturally a very weak character; used to being told what to do, her isolation from that influence through her father's death and brother's absence left her aimless and without purpose. Without her wits about her, any wanderings or danger that she got into would have been magnified.
The nature of the play itself, the circumstances in Ophelia's life at the time, and her own weak character were all things that helped to prepare the reader for her death. I hope that helped; good luck!