If anyone's interested, here's the text of the law she's charged under:
(c) The owner or lessee of a facility where a motion picture is being exhibited, the authorized agent or employee of that owner or lessee, or the licensor of the motion picture being exhibited or his or her agent or employee, who alerts law enforcement authorities of an alleged violation of this Section is not liable in any civil action arising out of measures taken by that owner, lessee, licensor, agent, or employee in the course of subsequently detaining a person that the owner, lessee, licensor, agent, or employee, in good faith believed to have violated this Section while awaiting the arrival of law enforcement authorities, unless the plaintiff in such an action shows by clear and convincing evidence that such measures were manifestly unreasonable or the period of detention was unreasonably long.
Not only does the law appear applicable to this case, but the theater management is immune from any resulting civil action. That's a really bad law.
I read section (c) as protecting, from civil suit, that particular employee who called the cops. I did not read that as protecting the owner of the cinema, who has instructed the employees to take those measures.
I am not a lawyer, and not a US citizen... I'm English, and in English law we have a thing known as "vicarious liability" which, unless I'm mistaken (and I may well be) means that an employee following a company policy is not held personally liable for the errors in that policy.
Rather, the law would hold responsible the employer who requires the employee to enforce unreasonable policies including, but not limited to, calling the cops if anybody sings "Happy Birthday" or so much as takes a photograph which may include a small portion of a copyrighted work.