It would seem the obstacle she cannot get round is that he makes it clear that she must either directly name the day or not indirectly get him to name it. This it is she cannot bear. In his proposals he goes up to this point, and stops there, and says, now, madam, it's your turn. And after all, give the devil his due, he's giving her 400 pounds pin-money (as they would have called it), and asking no portion at all.
I think it's in letters like this that Clarissa irritates many of her readers. She has said she has it not in her nature to press and manipulate, but this, it seems, is not because she finds it dishonest or ugly or manipulative, but rather because it's beneath her. She says her pride comes not from her thinking that she is doing thus and such in the face of the world or her husband, but because she is ever aware of the presence of God and acting before His eyes as if He were her mirror, her standard.
But if one looks carefully at her explications of this, it is always in terms of some game in which she is giving an advantage. We do know that any advantage given will be seized, and that Lovelace is eager for a sadistic enjoyment of her, so we sympathize with her in a way when she says:
I confessed that I had as much pride as himself; although I hoped it was of another kind than that he so readily avowed But that if he had the least mixture in his of the laudable pride ... he should rather wish ... to promote mine... (Ross Penguin, Letter 185, p 592)
He points out she doesn't show this laudable and Godly pride to her "implacable and unreasonable" family. It is only in front of him that she calls upon it, and as if Richardson was aware that the response to this is that a woman behaves differently before her family than before a stranger, that Clarissa is supposed to trust and obey her family; in the next letter (186) except that Lovelace hesitates about naming the day (which Clary could have managed had she wanted to marry), Lovelace offers generous proposals. He is the man she is to marry; she has agreed to live in the same house with him, acknowledge an implicit or provisional engagement.
So as the argument plays out it appears what stops her at this sticking point is not just this pride (which is fear of him) nor the integrity she professes at the end of the letter, but fear of the physical encounter which will come if she marries ("he ... grasped my hand with an eagerness that hurt it ... and put his other arm around me ... I was terrified!), dislike of marriage (ever so swiftly she's back "I want out of here pronto") and her sense she's better than him; he's inferior to her:
You, my dear, have accused me of having modestied away ... several opportunities of being--Being what, my dear?--Why , the wife of a ...
A reaction which combines a fear of sex with a contempt for Lovelace is at the heart of her refusal to name a day, at all to enter into his proposals. "I repulsed him" is what she writes; what man, what individual would not rage within at this.