I spoke to her teacher this morning and she told Adriana that she needs to tell her if someone is picking on her. But I also don't want my kid to become the tattle-tail
When your child tells an adult she is being bothered or harmed by someone else, she is doing exactly the right thing to protect herself. You shouldn't give this a negative spin by calling it being "a tattle-tail". Teachers can't always observe everything that is going on and your daughter should let them know if another child is giving her problems. This is one way that she can protect herself. Sometimes being a "tattle-tail" is exactly the right thing to do. The adults are there to keep her from being hurt.
I would not encourage her to hit or fight back. I would encourage her to tell any child who hits her, or pushes her, that she doesn't like to be pushed or hit and that she will not play with them or sit near them. She should have the right to avoid the children who are bothering her, and the teacher should allow her to do this. Let the offending children, even at the toddler stage, realize the social consequences of hurting someone else--other children won't want to play with them.
If your child is actually being used as a "punching bag" then the teachers aren't doing their job, or they just don't have enough adult supervision in the room. Toddlers have poor impulse control and low frustration tolerance. If they want something, they can tend to push, grab, or strike another child impulsively. If some children are doing this repeatedly, or if one child (like your daughter) is a particular target, the teacher should separate the offender from the group, at least briefly, to emphasize (to all children in the group) that such behavior is not acceptable, as well as to protect the other children. I am not talking about giving the badly behaved child a "time out", I am suggesting that that child be left in the room, but restricted to play alone, at least for a short time, at a special area or table which is at least several feet away from the other children. This table or area should have only a minimum of toys or playthings, so that it is clearly a less desirable place to be. In order to rejoin the group, the child must verbalize some understanding that it is wrong to shove, push, hit, bite, etc. any other child in the room. This method would also clearly show your daughter, and any other children that have been bothered, that something socially "punitive" happens to a child that hurts them--they know that an adult has tried to address the situation, and it is on a level that they can understand at that age.