On the sexual identity thing -- many queer people go through times when they identify as bi before declaring themselves completely gay. (This is why bisexuals often run into a lot of prejudice in the queer community -- they tend to be derided as fence-sitters and such.) Or they have heterosexual encounters before ceasing to have any sexual contact with the opposite sex altogether. Sexual identity is a spectrum, not a coin. So she may have had boyfriends or male lovers in the past, but if she identifies as a lesbian now, then she's no interest in men, now.
As for what "lipstick" lesbian means -- there's a Wikipedia entry on it, but, in a nutshell, it's a term for women who, like this version of Kathy Kane, are gay but who put forth a feminine image -- long hair, skirts or dresses, makeup, things like that. It's sometimes used to differentiate from "femmes"; in that case, lipstick lesbians are ones who are into other feminine women, but femmes are into more masculine-type women. That's not universal, however; my wife identifies as "lipstick", but she likes boyish/mannish women (she has a huge crush on k.d. lang). (And, yes, to clarify, I'm a guy; she's bisexual.)
As for the "cute" thing -- I don't see why she has to be cute. If she's an adult woman and a socialite, I'd expect her to be sophisticated first and foremost, and the way Alex Ross drew her posture and body language suggests just that. She's not another Cassandra Cain, after all. Yes, she's voluptuous, but there's muscle there, too. She really looks credible, to me, as someone who is athletic enough to be a crimefighter but still has curves to her.
And, I've already said something about tokenism, but here: if her being gay keeps coming front and center in a licentious or gratuitous way, then I'll be wholly instead of only partially disgusted with DC. I mean, it's true that a lot of queer people tend to have their sexuality be a much larger part of their identity than het people -- it's sort of part and parcel of being in a minority, especially one that isn't immediately obvious -- but that doesn't mean we have to have her make out with a woman every issue. (And I know there's going to be some people buying comics she's in just for that.) But if they're going through the trouble to establish this, I expect things to be done with it -- it may be too much to hope for to ask for a credible and honest portrayal of gay culture and community, or at least gay identity, but something at least approaching it would be welcome.
I mean, it's not like we're going to get a gay man with his own comic title out of DC or Marvel anytime soon. Not with the primary demographic that buys comics, anyway.