I have both good and not so good experiences that fall into this category.
Although my mom didn't "work" at my school, she did volunteer in the library and could be found there almost as much as the librarian. I loved it. There were no problems whatsoever.
My own grandmother was my Kindergarten teacher. That was actually pretty difficult for me. I was 4, she was super strict and held me to even higher standards than the other kids (I had to be perfect as a representative of our family). On the first day of school, she told me "You must call me either "Teacher" or "Mrs. _____, NOT EVER Grandma while in school." I adored my grandmother, but having her as a teacher was really difficult. She also drove me to and from school. "Bye, Grandma!", hops out of car, "Good morning, Mrs. _____!" A hard and weird transition for a 4yr old.
Anyway, since you won't be her actual teacher, it'll be fine. I had other friends whose parents were teachers at our school (at an international school in a foreign country, this happens pretty often) and they all loved having their parents at the school.