As noted in the first answer to your question above, Queen Gertrude hopes that the cause of her son's apparent madness may be his love for Ophelia. In Act 3, Scene 1, she says:
And for your part, Ophelia, I do wish
That your good beauties be the happy cause
Of Hamlet's wildness. So shall I hope your virtues
Will bring him to his wonted way again,
To both your honors.
However, in Act 2, Scene 2, when Polonius tells Claudius and Gertrude, "...I have found / the very cause of Hamlet's lunacy," Gertrude says to her husband:
I doubt it is no other but the main,
His father's death, and our o'erhasty marriage.
Evidently, Polonius' long explanation of his diagnosis of Hamlet's lunacy as being the result of his thwarted passion for Ophelia has some influence on Gertrude's thinking. When Claudius asks her, "Do you think 'tis this?" she replies, "It may be, very like."
So the Queen evidently would like to think that she is not responsible for her son's apparent madness, although she may still secretly fear that she is at least partly responsible.