I told her that if they made her change her shirt the school would have to not allow people to wear their crosses on their shirts or around their necks because that is a symbol of jesus' death.
I knew someone whose kid wore a t-shirt with motorcyle art and the number 81 on it to school. His teacher actually knew that it was a Hells Angel symbol and sent him home with a note saying the shirt was not allowed on school grounds, to which his biker father raised hell with the school at some kind of public meeting where parents and school board members were present.
During the course of the meeting they told him that since the number 81 was associated with the HAs, it was gang related and therefore not allowed.
The father countered that it was just a number, it did not orginate with the HAs but the school officials stood firm.
His last argument made quite the impression and caused people to squirm. He asked if kids were allowed to wear a cross and the shool people said of course they were. He said that the cross was a symbol of the KKK, a hate group, thus gang related and shouldn't be allowed to be worn on school grounds. The school official tried to say that the KKK were taking a symbol not of their invention and using it to their own end. At this the father asked what the difference was between the HAs using a number that they didn't invent and the KKK using a symbol they didn't invent and how could they discriminate against one but not the other.
He lost anyway, but it did back the school official into a corner that he could not get out of. It pissed off the "good Christians" in the audience but others praised him for pointing out the hypocrisy.