This is certainly not the case; Clarissa did not marry Richard--and reject Peter--so she could be the hostess of parties. This, though, was Peter's accusation cast at her. It may be a little unclear in the text because the narrator is reporting Clarissa's stream of consciousness recollection of Peter's remarks during a quarrel they once had:
How they argued! She would marry a Prime Minister and stand at the top of a staircase; the perfect hostess he called her (she had cried over it in her bedroom), she had the makings of the perfect hostess, he said.
Clarissa and Peter had different world views, different life visions. For instance, walking in a park Clarissa notices girls in pink frocks while Peter thinks of Pope's poetry and--more importantly--thinks of what is wrong with Clarissa's "soul": "It was the state of the world that interested him;... and the defects of her own soul."
Clarissa and Peter were forever embroiled in arguments because of their different visions of the world and life. These arguments were so scathing that they made Clarissa cry and never left her memory. Peter's accusation that she would be the "perfect hostess" was a judgemental statement of hyperbolic insult: he is saying that she is shallow to be interested in "the trees and the grass"; she should be interested in Wagner and a soul's eternity--like he is.
The fact that they are eternally separated from accord with each other is symbolized by the fact that he wouldn't put his glasses on in a park until she told him to: he can't see, doesn't want to see the colorful world she sees, and even if she points it all out clearly for him, he rejects it for abstract ideas. Clarissa believes she was right to have rejected Peter: "she had been right--and she had too--not to marry him."
On the affirmative side, Clarissa states clearly the positive reasons she married Richard: "For in marriage a little licence, a little independence there must be between people living together ... in the same house." In other words, Clarissa, like any self-respecting person, dislikes the continual arguments with Peter about what she should be; she dislikes the continual interdependence these quarrels create between her and Peter.
On the contrary, Clarissa enjoys the workings of her own mind; she enjoys the "beautiful day"; she enjoys the independence a respectful relationship and marriage can provide. Clarissa married Richard because she knows herself; she knows her personality; she knows her strengths. She wants respect for her inner being; she wants independence to be what she is and to do what she does best. It so happens, that because of her innate personality, because of her way of seeing life, she can make people feel important, cared for, and content. It so happens that she is an excellent hostess because of these valuable qualities. Clarissa values contentment and peace. Peter did and could give her nothing of contentment and peace.