I agree with Anna and Kimberly. Your daughter is only 3 and doesn't know how to express her emotions. Taking things away for several days is totally unrelated to the situation and she will not be able to make a connection between her actions and no toys. She's only 3. Taking away her toys and getting angry with her does increase her helpless and angry feelings that she's trying to work out. She needs to feel more involved and important in her life with you.
Hitting is normal at this age. And so is teaching not to hit. But I don't think that a child really understands this until they're older. It's important to stop the hitting. A good way to do this is, as Kimberly says, grab her, hug her, tell her we don't hit in this house and reassure her that you love her just as much as the new baby. She is not hitting to be mean. She is hitting because that is an instinct that we're born with. Each one of us had to be taught social skills so that we can get past our survival instincts. Every child goes thru a stage in which they hit. And everyone of us, even adults, have situations in which we feel like hitting but don't because we've learned there is a better way. Actually, some adults never learn that. We all learn best with positive attention and positive discipline. Hitting and taking away things unrelated to the hitting incident as well as anger teach our children that is the way to handle anger and in fact, makes them more angry, and more likely to continue hitting.
Understanding and calm, thoughful teaching helps her to learn a different way of handling her anger and reassures her that you still love her and know that she is a good girl who just needs to learn some new things.
Yes, some children do respond to being hit back, being yelled at, being sent to the corner without any follow up hugs or encouragement but usually that is because they are afraid of being hit again, etc. They stop their action out of fear and have not learned a better way. They also stuff their anger and it will come out in other ways, most likely sneaky ways that aren't so obvious.
Instead of putting kids with their nose in the corner I prefer providing a quiet time away from distractions. This may be a time-out but it's not punitive. It's a time to cool down. It involves a change of pace including turning off the TV until everyone is calm again. It may involve going to her room or being held my mama depending on the situation and how mama is feeling.
Involving her in the baby's care is important. Help her feel like the big sister who helps take care of brother. That gives her an important role and allows her to also be involved with mama and dada.
And time spent with one or both of you without baby brother is important too.
Bottom line is hitting is normal. Only twice in one month is good. And it sounds like the second time was partly in response to what happened the first time. Sounds like you were angry with her and getting angry back is also normal. Our job as parents is to teach a better way of dealing with anger while holding the line on a no hitting policy. We can do this more calmly and more effectively if we accept that what they are doing is normal and that they are still a good kid with good intentions.
This is a difficult task and I do sympathize with you. You do want the best for your daughter.