This is... Always kind of a rough situation. I don't know if I can help; maybe I can a little bit?
I came from a fairly screwed up family - my parents never, ever had a healthy relationship for a multitude of reasons. They split up when I was 4 years old, but had been sleeping with other people long before that. One of the things that happened around the time of the divorce was that my mother (who was in her mid-thirties at the time) came out of the closet as a lesbian, and my father re-married.
I didn't make too much of it at the time, being a child and truly not really getting it - I wasn't raised with any overt bigotry or prejudice thank god, and reality is so bizarre in the first place when you're young that you just have to take things in stride, more or less. So I was around a lot of lesbians when I was with my mother (and some gay guys but not many) and that was actually cool.
Fast-forward some years; I'm 12 or 13 or so and realizing that I'm gay myself, except it feels really awkward as hell. In part because my mother is also gay. You'd think that would make it easier, right? And in some ways it did, because I had very little anxiety about being rejected based on those terms by either of my parents. But... What I was fearful about to some degree was the idea that when I came out, it would somehow be... not taken seriously, because of my mother already being gay, maybe it would look like I was just emulating her for some reason, or that I was somehow 'made' gay because of some genetic thing, and that it would sort of be looked at some sort of extension of that.
And these ideas, they just upset me so much - because my sexuality felt utterly and uniquely mine, and was a private thing that had nothing to do with anything my mother did behind closed doors. I felt very defensive about this, and really didn't want to feel... patronized or not taken seriously. If you try to empathize with your sister for a second, it could be that she felt the same way. That you already being gay made things challenging for her in ways you may not entirely imagine. Not that I'm claiming to speak her, or tha my position is the same, I just thought it might be worthwhile for me to discuss. And it really *is* awkward to talk about this stuff with family, whether it's your sister or your mother or anyone in your immediate family, I think.
It still took me a couple years to sort it out and work it up to come out to my parents. The interesting thing was that while they were all very accepting, of course... Well, my father was actually more accepting than my mother. And I'm closer to my (straight) father, whereas my older (straight) brother is closer to our (lesbian) mother. Part of this has to do with sexuality, but I honestly think my mother was always a little dismayed by my homosexuality, to be frank. She has always made comments about me to "be careful" and talking about how terrible men can be and even making comments like she can't understand why I'd wanna be in relationships with men. And this is coming from a lesbian! I called her out on this, her acting like I had a fucking choice in the matter, and she stopped. But she still passive aggressively implies this stuff, and while she's gotten better about it, it took her a while to get there.
Whereas my father actually guessed that I was gay right as I was figuring it out, and actually pre-empted my coming out by telling me that just in case I happened to like boys instead of girls, it was absolutely fine and made no difference. He was always much more perceptive than my mother, and my father and I are very similar in a number of ways. He's never been dismayed about my sexuality. I have *always* found it easier to talk about boyfriends, or relationships, or anything personal with him. He's not judgmental about things, and it's just.... easier. I think the truth is that the gender gap is just so huge, and homosexuality in many ways only widens the gape. Thus, despite my mother and I both being homosexual, it is just so awkward and difficult for us to try and relate to one another on that level.
Anyway, sorry. This was long and probably boring. I guess my answer to your question, based on my own experience, is that it should be awkward. And you *could* always have a difficult time relating to one another in this way. But also, give it time! You too are at least of the same generation, and that changes a lot. She's still new at this and getting used to it. And when I say "give it time", I mean years. You can't put a clock on these things, or expectations really. Just be gentle, try not to push her initially here, and let things run their course.
) and begin to feel comfortable talking about yourself and your sexuality. 
