What would Ophelia say to Hamlet if given a chance?
The songs Ophelia sings in Act 4, Scene 5, help us to understand what events precipitated her descent into madness. She sings one song that goes
He is dead and gone, lady,
He is dead and gone,
At his head a grass-green turf,
At his heels a stone.
When she sings this, she seems to be thinking of her dead father, Polonius, who was brutally slain by her ex-lover, Hamlet, who she believes has gone mad. Polonius's death seems to have been the last straw for Ophelia's sanity, and it was perhaps her knowledge of his demise that broke her. Therefore, it seems likely that, had she a chance, she would ask Hamlet what it was that provoked him to murder her father.
When Claudius mentions her father, she changes the subject, as though it were too painful, and she begins to sing another song:
Tomorrow is Saint Valentine's day,
All in the morning betime,
And I a maid at your window,
To be your Valentine.
Then up he rose, and donned his clothes,
And dupped the chamber door.
Let in the maid that out a maid
Never departed more.
Ophelia seems now to be thinking of her relationship with Hamlet. If you recall, her father made her break off their relationship, believing that Hamlet only lusted after Ophelia and that he wasn't actually inclined to or free to marry her. She did so, and Hamlet took it poorly. When he is pretending to be crazy, he says all manner of mean things to her, including that he never loved her. Now, her song addresses Valentine's day and a girl waiting below her lover's window. The girl went into his room a "maid" (another word for a virgin), but when she came out, she was no longer a maid: she lost her virginity, then, to her lover. This seems to suggest that Ophelia might have slept with Hamlet, and so their relationship had progressed quite far. This makes me think that, if she could, she would ask Hamlet if he really did love her. It appears that their relationship went further than anyone else was really aware (she sings another song, as well, about a girl who had sex with a boy who then refuses to marry the girl).
It seems, then, that the two things bothering her the most have to do with her father's death and her ex-lover's faithlessness. She would likely, then, have wanted to speak with Hamlet about these two things. Ophelia may even have wanted to express her anger at Hamlet for his behavior toward her and her father.
It is difficult to determine what Ophelia would say to Hamlet if she could speak to him freely. Unfortunately, her father not only prohibits her from speaking to him but also requires her to return his love letters and break off the relationship without explanation. Further, it is Hamlet's own erratic behavior that likely leads her to acquiesce to her father's wishes.
If she had admitted to Hamlet that Polonius was listening to their conversation in Act 3, Scene 1, perhaps their relationship could have survived the challenges before them, and perhaps Ophelia too could have survived. If she had confessed Polonius's presence behind the curtain, then Hamlet would have trusted her, despite his budding contempt for women, which seems to stem from his mother's betrayal. Perhaps she could also have been a positive influence on him and prevented him from considering vengeance.
Polonius's meddling, and his position of power over her, prevents the audience from truly hearing her voice in the play. While we know from Hamlet and Ophelia's banter in Act 3, Scene 2, that they have established an intimate relationship and that she is comfortable holding her own in his verbal joust with him, we do not get to see the true potential of her effect on him.