IANAL. In
Santa Fe v Doe, that was not the only criteria. SFvDoe fails First Amendment tests on multiple grounds.
The decision behind SF v Doe is
Lee v Weisman where the principal selected clergy to offer prayers at graduation. Here, again there is official coercion in the form of an official of the school system sanctioning the religious practice. In part, the court found:
State officials here direct the performance of a formal religious exercise at secondary schools' promotional and graduation ceremonies. Lee's decision that prayers should be given and his selection of the religious participant are choices attributable to the State. Moreover, through the pamphlet and his advice that the prayers be nonsectarian, he directed and controlled the prayers' content. That the directions may have been given in a good-faith attempt to make the prayers acceptable to most persons does not resolve the dilemma caused by the school's involvement, since the government may not establish an official or civic religion as a means of avoiding the establishment of a religion with more specific creeds.
So it is the school's action in sanctioning the religious expression which is Constitutionally fatal.
Further more, in Santa Fe v Doe, the court found:
The delivery of a message such as the invocation here--on school property, at school-sponsored events, over the school's public address system, by a speaker representing the student body, under the supervision of school faculty, and pursuant to a school policy that explicitly and implicitly encourages public prayer--is not properly characterized as "private" speech.
And,
The policy involves both perceived and actual endorsement of religion, see Lee, 505 U. S., at 590, declaring that the student elections take place because the District "has chosen to permit" student-delivered invocations, that the invocation "shall" be conducted "by the high school student council" "upon advice and direction of the high school principal," and that it must be consistent with the policy's goals, which include "solemniz the event."
The court makes very clear that the school's sanctioning of religious expression is what makes the religious expression fail Constitutional tests. They specifically reject the claims that
personal speech is involved when the school specifically provides for the expression.
With regards to the captive audiences:
The school district's supervision and control of a high school graduation ceremony places subtle and indirect public and peer pressure on attending students to stand as a group or maintain respectful silence during the invocation and benediction.
...
Since adolescents are often susceptible to peer pressure, especially in matters of social convention, the State may no more use social pressure to enforce orthodoxy than it may use direct means.
Again, the court is clear that it is the school district's specific provision for religious expression which is fatal.
This is not what is happening in this situation. In this situation it
is private speech, uncoerced and unsanctioned by the school. Indeed, the school intially tries to forbid it. Furthermore, as it is clearly private speech, the student has First Amendment rights to make that speech. The school system made the correct decision in allowing her to speak on whatever she wanted.