I'd describe her state of mind as troubled, stuck in a bad marriage (now really stuck with a baby) and maybe in a kind of mid-life crisis. If you're referring to dinner in the first chapter, Daisy is initially over-the-top which reveals she's acting; or, considering she's dealing with Tom's infidelity, she may just be happy to see an old familiar face (Nick).
"I'm p-paralyzed with happiness." (13)
Daisy later compares Nick to a rose, and he interprets it this way:
This was untrue. I am not even faintly like a rose. She was only extemporizing, but a stirring warmth flowed from her, as if her heart was trying to come out to you concealed in one of those breathless, thrilling words. (18)
Daisy storms out. When she comes back, there is no hidden subtlety. She says she's had a rough time and she's cynical about everything. Then she says something that implies the idea that everyone (at least in her circle) thinks things are bad.
You see I think everything's terrible anyhow, she went on in a convinced way. "Everybody thinks so-the most advanced people. And I know. I've been everywhere and seen everything and done everything."
Nick interprets this as a mask for what is really troubling her: namely, Tom's infidelity and I always thought she was sorry she married Tom for other reasons: his glory was done (a former athlete) and he filled that void with women and his own racist view of sociology which made him feel intelligent.