It's hard to say without seeing a situation & knowing whether we are talking a reprimand, yelling, or merely a loud tone. Some children are more sensitive & that is something you work on long term, it isn't fixed at 3. If a teacher is actually yelling at 3 yr olds, I'd look into speaking to administration about that. It's not appropriate or necessary to yell at small children. She may also simply benefit from having a warmer teacher if this one is rather stand offish. Some kids need that. My middle child does. It's his nature to speak softly when intimidated, be easily scared by loud voices (even when it has nothing to do with him), hates anything scary at all, etc. It's the way he's been since infancy. I recall a game another child of mine was playing on the TV that was a Mickey Mouse game, but it has an ink blob scene, where the ink blob comes to life. He was only about 8 months old & he lost his mind. He went into shaking, shrill screaming, and when I picked him up he was climbing me. Some kids just are much easier to scare. It's okay. Life is full of all types & all of them have their attributes, even in this situation. He is also the most thoughtful of my children now, he is always very aware of what is happening in a given situation, he's been a very cooperative child as he doesn't care for any confrontation, etc. The downsides I find I have to work with is to use his voice, talk louder, be heard. I try to coach him on standing his ground when he should, so people don't take advantage of his wish to avoid a confrontation, and I have worked with him on taking some risks & seeing that he can handle it.
It's really a lovely quality in a person. Most things can be, if we find the things it's linked to. Often people exhibit groupings of characteristics that are intertwined. So for sure, work with her on it. Just be patient & realize that who she is, is good on it's own. We are just there to help our kids be the best versions of themselves, but they do arrive with a preset personality taking shape & the older they become, the more aware we are of the various nuances & complexities of this personality they have. I would not worry though. A sensitive 3 year old crying when corrected is a normal reaction for a child with that personality. It will be something that improves with age & a little work & confidence building.
One of the most effective things I do with my kids when small is affirmations. So each child has their own set & it is said together every morning & night as a way to help them remember their own strength, bravery, empathy, kindness, compassion, integrity, etc.
Learning to master the weak points in your personality & to develop the strong points is a lifetime endeavor, one you hopefully never cease, even when you are one day a grandparent. So just know that it's okay, you have time, she will find her voice with a little help & just like you don't make a high needs baby into a high needs baby, you also don't make a child timid that isn't that way internally (of course, barring obvious things like severe abuse, etc). She is also old enough to do some super simple role playing, like asking her to be the teacher while you are a student. Watching how she behaves as the teacher will allow you a window into seeing her life from her own eyes. Pay attention when you do this. It tells you a LOT at this age. They are too young to try to hide anything, so what you get in teacher role speaks volumes as to what she thinks teachers are like.
Good luck. The great news is I blamed myself for EVERYTHING that was "wrong" with my 1st child. Then I had a 2nd child that was nothing like him. I figured out I am not as all powerful in forming these kids as I thought & then another came along & only confirmed that by again being nothing like the other two. I found it a great relief to realize I am not entirely responsible for every nuance of who they are. I probably should have known that though. I come from a large family myself, all the same mother & father & NONE of us are terribly much alike. We are all solid people with good family lives, etc, but beyond that, we live very very differently, like very different things, some are the type to steal the mic & dance on stage & others would rather sit in a corner & go unnoticed. I wish I had really thought about all that before having kids. It helps take some of the stress off your shoulders. <3 Much love to you!