Promo

This morning I went into work, and my manager told me that instead of waiting til next week, she wanted to talk to me, "now."
So I went over to her little "office" which is really a desk behind a wall behind customer service behind the check out area of the store, so it's not very enclosed. She started off, "I know we talked about interviewing for the supervisor position, but I talked to my front end staff, and..." I immediately prepared myself to hear her say that they didn't think I was a good fit, or that they had chosen someone from outside the store, who would be a perfect supervisor. But she went on, "and we decided to hire you and your coworker the promotion, and give you each one of the nights to supervise, so that we will have more people to cover shifts if one of the other supervisors needs a vacation or the night off."
Nice!!! So, I get a promotion, and more money, and more responsibility, yay, and don't have to worry about competing with my coworker.
Except that a few hours later, I was standing at my register next to a girl who has worked at the store for almost a year, and who was complaining about needing her review. After which she would receive a small raise. Our boss had promised all week to do the review with her, and today is the end of the week. And she walked out, without even a mention of the review. Which pissed this girl off, understandably.
Thennn my fellow promotee came in on his day off to pick up a pay check and some food, and said to me, "Hey! Did you hear the news?? I even bought a bottle of wine to celebrate!" and then left.
So my register mate turned to me and asked what he was talking about, and I explained that the two of us were being trained to be supervisors. Her face changed from curious to cold and angry. She was like, "Really. That is surprising." I had someone at my register, so I turned to help them, and when I turned around again, she was still looking shocked, and told me just how surprising it was that they'd decided to promote the two of us, when we had both just started there. "Especially him!" she said. "He is so negative about getting things done at closing time! I can't believe they would do that..."
Clearly she was upset that she had never become a supervisor after all the time she has put in there, but what was I supposed to do? The job was posted on the board in the staff room for all to see, and all to apply for. If she didn't look at it, whose fault is that? Certainly not mine. I just stood there in front of her, unsure what I was supposed to say, and unclear whether she realized that she was making me feel bad for something I had been pretty pleased about. So instead of responding, I just... awkwardly walked down to the other side of the room and helped someone else bag up their stuff.