She doesn't treat me the same way she treats you. Have you ever been in a friendship where a game of favorites was being played?
Even when I was younger, I never liked big groups of friends. I preferred to have one absolute bestfriend, a few close friends, and some acquaintances. I usually kept my hangouts small (one or two people) and would prioritize according to the deepness of the friendship. (If my best friend and my acquaintance were both having a party I'd attend my best friend's and set up another hangout date for the other person)
But when you're young, such as in junior high, the idea of a tight group of friends is appealing. A bit like sex and the city, you have more than one person to lean on, spend time with etc. It was around my preteen stage that I decided to test out group friendships and having more than one best friend.
However, psychologically we connect better with some people more than others. Perhaps we feel more free to share with them, have more in common, or have a better time. Even in a group of four friends, you'll have that one person you feel most connected to. That doesn't mean you don't all get along but you may not interact in the same way.
Of course when you're young you don't understand this and I didn't always see the slight favoritism that can happen in friendships.
When I was young, I was very close friends with two girls. Both were important to me and neither was more my friend than the other. But one day one of them confessed she was having a hard time in the friendship, because she felt our friend was treating me better.
I didn't see it from my friend's point of view at first, but after a while I started noticing little things that confirmed my friend's suspicion. Our mutual friend had a tendency to react sweeter towards me, share more with me, and invite me out me more often. This caused a tension between me and my hurt friend where a jealousy built up to the point where my friend said she no longer wanted to be friends with either of us.
At that point, I was very young. Too young to know how to fairly deal with the situation. But as I got older I realized many people go through this and even encountered it when I was a few years older.
The second time it happened, I asked my friend why she treated me different trying to explain how it hurt our other friend. She said she didn't notice a difference--that she liked us both the same. But her behavior contradicted the claim. Interestingly enough, I ended up being closer friends with the girl that felt left out.
Recently, I find myself in a similar situation. And have begun to notice a pattern when it comes to these situations
1. It's never simple one thing. A serious of events take place that the jealous person notices. As these little moments build up so does the tension.This habit of letting it slide until you're ready to burst makes it difficult to approach the person hurting you. A problem that can be fixed early on, turns into a large fight that leaves people deeply hurt.
2. The jealous friend rarely confronts the friend playing favorites, instead they confide in or even take their anger out on the favorite friend. In one case, I was the new friend and was accused of trying to breakup the friendship. While I don't oppose saying something on behalf of someone else if the situation does concern you, I believe more that people need to talk to the person that is actually hurting them. There is no possible way someone can know how you feel unless you say something. If you are not sure how to go about, let someone help you come up with a diplomatic way to address the situation but it has to be you that expresses your feelings.
3. The favorite friend may wrongly take sides or passively sit in the middle. It can be easy to see one side more than the other, but this puts you at the risk of ruining your friendships. It's also not always best to have an "oh well" attitude. In all vain honesty, it's nice being the favorite friend but it doesn't feel nice to lose a friend over it. It's a good idea to let your two friends have some one on one time. They may need to rekindle the friendship. Also, bring it to your friend's attention that they do play favorites and it makes you feel uncomfortable. Sometimes a person is doing something wrong and they don't even know.
It isn't wrong if you connect with one person more than another, but it's not fair to blatantly treat someone as if they aren't as special.