What do we know about Ophelia's mental state by the end of Act IV?

Scene 5

Back in the court of Denmark, we see Gertrude speaking with a gentleman who explains that Ophelia has gone mad. She is rambling nonsensically about her father and insisting on seeing Gertrude. The queen reluctantly admits Ophelia, who proceeds to sing a number of simple and haunting songs, some of them quite bawdy. The king enters and witnesses her madness. Ophelia then speaks openly of her father’s untimely demise and hasty, unofficial burial. She threatens, “My brother shall know of it,” and exits.