I think you are grasping at straws. The two examples you state are mutually exclusive, the church has never railed against someone merely being a homosexual, and the other is clearly a violation of civil law.
What is going here is much like a merchant in a free society stipulating requirements against the law, before transacting business. It is much more like the phone company demanding that you convert to islam, before allowing you to connect to their service. The law should come down hard on this school and demand that they cease and desist, as this parent has committed no crime. If this comes to trial, it is my opinion that the parent will win, and it will be determined that the school never had the right to demand arbitrary behavior beyond what the law currently demands.
Your first sentence is oxymoronic. A merchant in a truly "free society" shouldn't be restricted by "law" in what conditions are necessary to do business with him.
This church has every right as a private group to restrict attendence to their school.
That said, I think their attitude is stupid and un-Christian. Had they truly ministered to her out of love, kept her kid in school, and been supportive rather than condemnatory, they might have saved the mother.
But then I don't have to hang around either of them, do I?
Nowhere in God's law is a homosexual or fornicator going to inherit the kingdom of God and explicit direction is given for qualifications of leadership within the Church. Every God-fearing church discerns between those who violate those discerning guidelines and those who abide by them.
As a reality check, the recent newsworthiness of pedophilia charges in the priesthood indicate the Church very much believes such activity is grounds for removal and disassociation. (It wouldn't be a scandal if it was considered acceptable.)
No civil law has been violated. A conditional covenant was entered into by the two parties wherein one party violated its conditional terms. The abiding party therefore is no longer bound to the covenant.
The conditional terms were based upon Scriptural guidelines and any attempt by a civil court to rule on the Scriptural merit of that condition now places itself to be judged by the standards of God's justice.
In the counterexample provided where an Islamic God becomes arbiter, a nonexistant god is mute, while in the case of Scripture, if the the court intervenes it will become subject to omniscent judgment over time.