N.,
A baby is never to young to have limits set. As soon as my son started scooting/rolling all over the floor, he started being taught the word "no." But "no" does nothing without an action. That action does not need to be a slap on the hand or thigh or rear, but it can be moving the child across the room away from whatever the issue is. After a few times of moving, my son would normally throw a fit and just sit and cry. I would let him throw his tantrum alone for a few minutes. I didn't do it to let him cry, but because tantrums are not acceptable either. He is still young so a minute or two is long enough for "alone time" in a time-out or semi-time out time so I would go and comfort him after walking by him and getting out of sight for that moment or so. This was a hard thing to do, but it has really helped. Most times all I need to do is say something and he will stop. It usually takes a couple of times to get him to stop and go away from it, but that is an age related behavior that will change as he gets older.
In addition to trying a time-out situation and any other techniques you may decide to try, you need to be sure that whomever cares for your daughter is on the same page as you. If she is in daycare, and you can do this, try to stay one day and observe how she behave there and what the teachers do with bad behavior. If it is ignored and she runs wild the whole day, a change of daycare may be a big help. If she is with grandparents, make sure you speak with them about what you are trying to accomplish and encourage them to continue about things the same way you are (so she gets consistency) for the time being and then they can adapt to the ways they prefer as she gets older and can understand the differences are OK, but she has to listen no matter what. Be sure to come about the issue without seeming like they don't discipline at all because they will definitely get their feelings hurt, but do come about it in a self-directed way so that they feel like they are helping you.
Take care, and remember, as my mom said, "I'm bigger and smarter and if it comes right down to it, I can just sit on them!" FYI,she never had to. ;-)
M. M.