Then she has a grievance against the school system, and should seek compensation if dismissed based on that.
Private companies can require any skill they so wish from a prospective employee before they get hired, they are after all private companies, and every level of government may need people who can communicate in a wide range of languages. In that case, they can require proficiency in a foreign language as a pre-requisite of employement. If your relative was hired for a job that required a certain level of proficiency in Spanish, and she can't perform at that level, then the employer has the right to terminate, if that's not the case, she needs to get a good attorney, and sue the pants off that school district.
If a company clearly states up front they are looking for bilingual skills, that is one thing. But it sounds as though the lady in this article had worked there for awhile before the requirement was put in place. In cases like that, it is up to the company (or government agency) to provide the training needed to get the employee up to speed. (In my opinion, this training should take place during work hours.) The employer should ALWAYS foot the bill for such training if the requirement is instituted after the fact.