K.,
Congratulations on the new baby! It sounds like your daughter is a little jealous of all the attention the baby is receiving from you. It's natural for siblings of newborns to act out just the way you've described. She still wants to be taken care of just like before the baby came along. In her head, the way to get that is to act like the baby. I went through something similar with my own kids. My son was 5yrs old when my daughter was born.
You need to incorporate a few things into your schedule:
First, bedtime rituals or schedules should be kept as much as possible. Think about it: the baby has disrupted your little girl's world in just about every single way. She needs the security in knowing some things are going to be the same--unchanged. If the baby needs to be fed, feed her wherever you usually read bedtime stories.
Second, children up until the age of 7 need their parents to help them brush their teeth. When she gets to be about 5 you can simply supervise. Until then, you or your husband should be brushing her teeth. It will give her the attention she is craving, give her the foundation she needs to keep healthy teeth all her life and keep the peace in the house.
Third, try, try, try to stop yelling. Is it working at all for you now? No. Time outs really work. Experts suggest that the time spent in time out coincide with the age of the child. Therefore, she should spend 3 minutes in a corner or a seat away from anything that could be fun. Make sure you are able to see her. Talk to her and explain simply that we don't (do what she did) in our house. If she does it again, she goes back to time out. Make sure you welcome her into the activity as soon as she comes out of time out. She did her time, now all is forgiven.
Next, you and your husband must carve out some time from your busy schedules to spend one on one time with your daughter. This time alone, focused on her (like the good old days before baby) will not only give you a break from spit up and diapers, it will make her feel important again. Take turns once a week (or more) and take her somewhere. It could be after dinner to get an ice cream, a walk, a drive or a visit to the playground. She needs to know you still love her just as much as the baby.
Last, make sure to praise her for helping or doing things on her own. This is so important! She needs for you to be happy with her. She wants your approval. So give her simple tasks to complete like putting trash in the garbage, getting diapers or wipes, finding a toy to distract the baby while you change the diaper, etc. You will see a difference in her behavior if you change first. No child wants to hear yelling all day just like you don't want to be yelling all day. Right? Remember that our job as mothers is to be the heart and center of the family. We must find a way to make our homes a safe and welcoming place for all who live in it.
I know it's difficult right now, but I can tell you it gets better if you try to see things through your daughter's eyes. Remember: She loves you. You love her. God bless you and your family!