<human>: Can you condense the text into three sentences or less?

I'm [21] she's [20] (let's call her sally) I think this is a fairly common problem people face (of either sex) but here goes, details:

While at her birthday party a few nights ago, I was introduced to her older sister. All a bit drunk, she told me that she already knew who I was (because sally was talking about me earlier that night, which I would think to be good news) More to point however, she then continued to tell me to be careful though because sally's a bit 'weird' when it comes to relationships. Of course asking her why she says that, I got a quick response, something along the lines of, "she's never had a really decent boyfriend. She's only dated a couple of guys and although she dated each one of them for quite awhile, none of them were exactly nice to her." I didn't really like hearing that sort of thing while at sally's birthday party, so i dropped the subject and wandered elsewhere and tried to enjoy myself while the night was still young.

I think my biggest concern is that she may not really know what she wants in a relationship. Because of that, I feel more inclined to be a bit standoffish but that seems counterproductive on my part. I really like her, a lot, but I'm really at a loss as to what I should do.

I also feel as though me knowing these things about her life, really isn't appropriate yet and at the same time beneficial to me.
<bot>: What's some good advice when dating a girl who hasn't really dated decent people before / and should I be worried that she may not know what she wants in a relationship?