Speaking from my experience of helping a few little girls grow up (as their nanny-- and chiming in from this perspective since I have a boy)-- I think there has to be a balance of when to offer coaching/social correction and when to let things go.
The preschool teachers should be addressing this in the moment, and then, as others have suggested, just offer reflective language and support when she comes to you with her stories of the day. You do want to keep her perspective of reality in mind when talking to her. "So, you felt like.... I wonder how that felt to Sally?" Ask questions which encourage empathy.
Here's the other thing-- and I saw this most especially with my own son: the early years of elementary school seem to be a time of 'sussing out' what friendships really are. My son would come home, bummed "Johnny isn't my friend" -- all because Johnny got tired of playing SuperKitties and wanted to play a game with other friends. Little kids tend to interpret small choices such as who they played with at ONE RECESS as 'best friend/not my friend' enormity. This is something they have to consciously experience and will likely, eventually grow out of. I saw, in his first grade classroom, three girls who would jockey for position with each other, usually on girl was bestowed the 'power' in their relationship. Again, there is some balance required-- the teacher would let them sort it out, up to a point, and then just make decisions for them. (such as who would sit with whom, etc) They really needed help.
For what it's worth, it wasn't until my adult years that I learned how to be a good friend. I had lousy models in my family for that. I sure hope that you will be able to see that some of what your daughter is doing/experiencing is just part of her juvenile development. I find that when I see behaviors which make me uncomfortable, to try to reflect WHY they cause such unease. Once I've done that, I can usually be more objective (separating my feelings from my child's actions) and handle the situation better. For what it's worth, when I look at 'four year old development', under social/emotional -- tattling is in there. Judging from my son's classes, too, I think it will be present for quite a while. So, encouraging her to "talk to your friend first, and if what they are doing is unsafe, tell the teacher, or you can go play something else" is a good way to go.
Good luck!