Okay, first things first- why is she 3 years old and still in a crib???? She really should be in a toddler bed- it's not safe for her to be in a crib anymore because she can try to climb out and fall and hurt herself. I know you're thinking at least the crib keeps her in her room at night but you really need to move her out of the crib. If she won't stay in her room, you can put up a baby gate at her door. Eventually she'll "get" that she has to stay in her room at night.
Now, as far as the waking at night, she's doing it because she knows you will come and soothe her. Better yet, she knows you'll put her in her bed. It's time to do the same thing you did when you first started putting her to bed without any rocking, etc. Just put her to bed around 9pm, bring her in, turn on her nightlight, give her a kiss and hug, tell her goodnight you love hre and you will see her in the morning. Don't let her dilly dally or ask for this blanket, this animal, this light, etc. If she gets up, you have to ignore it unless you know she is in pain. She will eventually stop when she realizes you aren't coming to rock her or move her into your bed.
I know it stinks because you're afraid she'll wake the baby, but you have to do this or she will keep doing it and you'll end up like my parents- with my brother sleeping on their floor until he was like 10 years old! If the baby and her share a room, move him into your room for now and make sure the door is shut and you can even get a white noise machine or turn on a fan to help him drown out her screaming if she is doing that.
I hope this helps.