Is it normal for my brother's girlfriend to be so judgmental?

I apologize in advance for the Bible you are about to read.

Let me first say, I think of myself as a generally intelligent, sweet, young woman. I dislike being mean, and I feel terribly guilty when someone is upset with me.

I have three brothers. One is fourteen (we'll call him R), one is seventeen (we'll call him A), and one is turning twenty this month (we'll call him G).

R has a wonderful girlfriend, and they've been together for almost a year now. They're a cute couple, and I absolutely adore her.

G also has a sweet girlfriend, and they've been together four years, I think. She's a very nice girl, as well.

And now, we come to A's relationship. They've been together less than a year. I honestly have no problem with his girlfriend. She's pretty, and she seemed nice, and even reminded me of myself at first, personality-wise.

One day, I was over at my mom's house, hanging out with my family. And my brother, A, comes out of his room, claiming his girlfriend does not like me. And I'm thinking, "What? Why? We have barely talked at all. I never did anything to her. I don't want her to dislike me. Did I do something to wrong her?" Etcetera.

Anyway, since she was over at the house during that time, A would not tell me diddly squat.

I confronted him about it later, hoping it was just a joke he was playing on me. Turns out, she has plenty of reasons to dislike me.. But they are reasons that have nothing to do with her.

First reason: I don't go to college.
Second reason: I don't have a job.
Third reason: I'm only 18, and I am engaged.
Fourth reason: I occasionally drink (at social gatherings, when the situation permits).
Fifth reason: I smoke a few cigarettes per day.

I can reasonably, and logically argue all these reasons in my favor. Not just because I am good at debating and turning my thoughts into coherent concepts, but because my reasoning on most, if not all of my actions is completely justifiable.

Honestly, I don't know if I should try to make amends with the girl or not. I am just extremely annoyed after finding all this out. But at the same time, I feel bad. I really want her to like me as much as R and G's girlfriends do.

And why would she tell my brother, of all people? Of course he is going to tell me, even though she told him not to. I wish she could have come to me first, so I could just clear it up there. But now I am debating whether or not I should even attempt it, or if she will just continue to dislike me no matter what I say to her.

In conclusion, is it normal for such a seemingly sweet girl to be so judgmental of someone she barely knows? Shouldn't she just automatically like me, because I am her boyfriend's sister, and he loves me as such?

Should I be this bothered by it, this annoyed in knowing that a single person on Earth dislikes me for reasons that are out of her hands? Should I be aggravated enough to type out such a long, well-detailed recollection of such events, just so some anonymous internet dwellers could comment and troll as they see fit?