The fact that the County Board of Supervisors chooses to hear certain prayers and chooses not to hear others is note establishing a religion.
In your scenario, anyone and everyone can make something he/she calls a relgion and demand to be heard.
That's utterly ridiculus.
It is a use of government time and resources for the benefit of only certain religions. That means, the Wiccan woman in question, as a taxpayer, is having some of her tax-money spent for the benefit of another religious group while her group does not receive the same benefit.
In your scenario, anyone and everyone can make something he/she calls a relgion and demand to be heard.
That is exactly what I'm saying. If the board has a problem with this, they can simply discontinue this practice.