She didn't try to shove anything down anyone's throat. The school has no right to force same-sex couples to pay more for their prom tickets than heterosexual couples have to pay.
Lesbian Teen Speaks Out on Cancelled Prom - The Early Show - CBS News
Personally, I don't think there should have been separate prices for individual tickets and couples tickets. That isn't very fair to anyone who doesn't have an opposite sex date.
And she was further discriminated against when they told her she and her date would have to arrive separately and leave if any of the other students were uncomfortable with them being at the prom. I didn't see the stipulation that other students with "individual" tickets had to all arrive separately. And the other students do not have a right to not be uncomfortable. If they did, then I bet there would be a few more couples that could be asked to leave, since there are plenty of heterosexual couples that make others "uncomfortable".
As for the tux, she has every right to wear an outfit to prom that is deemed appropriate for guys to wear. Her wearing a tux, or even a guy wearing a dress, does not disrupt the learning environment (since there is no actual lessons occurring during prom) nor does it affect the safety of the students nor it is a promotion of an illegal activity. The cases in the past upholding school dress codes, did so based on one of those above principles. And it has been said by the SCOTUS that students do not "check their rights at the school doors". Therefore, it is a case of gender discrimination. Even if she were straight and just asking to wear a tux, it would still be gender discrimination.