It does not matter. If the girl was allowed to stay in school-knowing the family situation. The school is giving tacit approval of the homosexuality to the other students. Apparently, Mom decided to come out of the closet with this girl, but kept quiet when the older girl was in the school. This is merely pushing an agenda and using her own daughter to do it. The school where I live will not accept the children of couples who live together-sexual sin is sin...period.
The school has a right to admit or deny whomever they choose and I support that 100%. My argument is, did they handle this like they should have? What about the student that father is having an affair? Are they kicked out? or Does the faculty and administration support and lift up that student? If the issue is that the School did not know at the time and now they do, what about all the times they find out about various sins of other students parents? I would think that that will be easy for them to get dinged legally for applying the rule differently. Plus the school by expelling the daughter has been the one to spread this about this students mom and partner. (yes I am against homosexuality)
Let look at it this way....
School finds out, takes child aside and says, we have concerns that your "mom" might not be living the moral life that she agreed to when she enrolled you in this school. We want to ask you if you intend to follow and adhere to the code of morality that you signed here? ( detailing out what qualities and behaviors that means) letting her understand that we would not allow her mom to participate in functions with her partner. But as long as you are striving to lead a Christlike life we will welcome you here and whatever we can do to help your mom come to a realization of where she is in her life we want to do that.
Now which one is handled with more of a Christ Like attitude?
This situation was handled poorly from the following perspectives.
Morally
Legally
PR wise
Logically