This cute little girl (well, not so little she was old enough to fall in love, but her mother perceive her as a little girl saying all the time about things that have and haven’t to be done), is a daughter of tyrant mother Lady Bracknell and Algernon’s cousin. She is submissive to her mother in public but rebels in private. Also, in the book, she appears as a big love for Jack. She is the hugest object of Jack’s attention and desire.
But as she is in love with someone else (as she thinks), she refuses his love that is why we see her as self-centered and flighty. She leads herself like Cecily; she also wants nothing else but to marry a man named Ernest. It sounds strange, but after reading the text, you will get it even more clearly. It would be funny if not so sad; she is totally I love with a man called Ernest, who in reality is Jack.
Gwendolen is a model of what is a high fashion in the society of that times. She is demonstrative of some sophistication and confidence which existed in London socialite. That socialite believed that style is the most important thing, not sincerity or intellect.
She leads herself like a very important person (maybe her mother’s influence was too big to understand it). Gwendolen speaks with a tone of authority. But it changes when she sees someone else, so her attitude changes on matters of taste and morality.
Though, nothing could be so bad. She is intellectual, cosmopolitan, even kind and utterly pretentious (we find it an advantage rather than disadvantage). Gwendolen is totally fixated on the name Ernest. After the meeting with him, she keeps saying that she will not marry anyone else, especially if the person has any other name as Ernest. She is totally obsessed with that name.
By the way, she changes her mind and agrees to marry Jack even despite her mother’s disapproval of his origins.
Hon. Gwendolen Fairfax in the Essays