Complaining...hmmm...
How about "Come, let us reason together." It sounds like these folks were taking a stand for righteousness. That said, it seems apparent that this Catholic school is lost. If I were this family, I would look at this child being kicked out as the mercy of God's hand. He's probably getting her out of there before it's decimated by God's lightning bolt of judgment. Where are the other parents in this thing?
You know, the reverence for God and Jesus and the Holy Spirit has been so eroded. I hear the lady (Catholic, by the way) across the way from me say the Lord's name in vain, as a swear word, about five times a week. I have said, "please don't do that." But it is such a terrible habit with her, and she doesn't understand the gravity of it. I, myself, am just really beginning to understand the many ways I treat God irreverantly, and how very serious it is.
Christians out there, could we agree to pray for this for our country, that the Holiness of the Triune God would be made real to hearts in this country, and that our attitudes toward Him would be impeccably respectful, reverential, and that we would have a holy fear of Him, which is the beginning of wisdom.
The real point here is that it is a private school and if she doesn't follow their rules, no matter how she feels about them, the school would have every right to ask her to leave.