Way back in high-school, there was talk of my school going year-round and establishing a dress code with uniforms. The year-round thing didn't bug me, but the dress code sure did. I've been a t-shirt and jeans guy since the 6th grade, and being told that my standard of clothing was now inadequate ticked me off. I'm a simple person, and I like simple things. A daily uniform seemed a bit much. I was in the band, and to me a uniform was to be used for a purpose. It set you and your group apart from people on those occasions you wore it. Wearing a school uniform every day cheapened the idea of a uniform to me. What's so special about it if everyone's wearing it?
In a professional working environment, I understand that you need to put on a little bit of a performance. You have to "dress the part," as it were. I generally have no problem with that, as long as "the part" is reasonable and doesn't have a bunch of stupid rules attached to it that have no meaning. My philosophy is, as long as you look decent and presentable, you're fine. All else is up to you.
For your friends specific case, it is extremely inappropriate for her school to even mention that she has a tattoo. The school should be playing her up as a qualified individual that other schools would want to hire. It should then be up to those schools to decide through an interview if she's appropriately attired and presentable for the job. From your description, her tattoo probably wouldn't even be noticed, and thus completely irrelevant. If it were visible, it would be relevant, and the school would have to decide if it is or isn't an issue based on what it is, where it is, and how big it is. Like it or not, those are relevant things to consider. You wouldn't want a teacher with an erect penis tattooed on their forehead teaching your 3rd grader, would you?
While I have my own reasons for disliking tattoos, there was one teacher I met who had appropriate tattoos. He was a Hawaiian Studies teacher that traveled from school to school, and he had Hawaiian tattoos on his arms and face that were clearly visible, and he had some on his legs and chest that weren't visible. If you've never seen Hawaiian tattoos, they generally are patterns using lots of triangles
. As a Hawaiian Studies teacher, this was both appropriate and meaningful. It enhanced his teaching, giving him an air of authenticity and authority, rather than detracted or distracted from it.