If your kid is interested in composing/theory, yes. If not, it may not be much fun. As others said, it won't really get you any credit. But if kid is interested in a college music program, it can be a good way to help demonstrate proficiency.

Can you or your kid talk to the teacher and inquire about suitability?
My kid, who also had many years of piano, took it in 9th grade and got As in the class and a 5 on the exam.
They needed their private teacher's help with one or two concepts, but otherwise didn't find it overly challenging, and it was their favorite class in 9th grade.
They felt the most important pre-req skill was the ability to read music well, and some basic understanding of scales/keys, chords, etc.
But like every HS class, it will depend a lot on the teacher.

My DC with a similar musical background self studied and got a 5 on the exam. Although I guess self study doesn’t help if your DC wants to take the class for their art credit…. Anyway, I think with that background, your DC will find it manageable.

Ask the music teacher at your school. Ours advised that it was a difficult course which historically sophomores do not score well on the AP Music Theory exam compared to juniors and seniors.

Why take the AP version? Does your child want to major in music? If so, their college will want them to retake the first semester of music theory with them. If your child doesn’t want to major in music, why not join an ensemble class?

Is this a good course to take to get the fine arts credit ? Is it a lot of work?
Kid has 8 years of piano (level 7 trinity piano exam pass), chorus and musical theatre experience.