Is it legal for a teacher to give you a zero for not showing up to a 6pm activity and having to do an alternate project on top of that PS. its my art teacher and she forces all her students to show?

In general, teachers have the discretion to set attendance and participation requirements for their classes, and they can enforce penalties like giving a zero for not attending a required activity. However, if this policy was not clearly communicated in advance or if there are extenuating circumstances, you may have grounds to discuss the situation with the teacher or school administration. It's important to review your school's policies and any guidelines provided by your teacher regarding attendance and grading. Open communication with your teacher about your situation may help resolve the issue.