Is proper grammar an indicator for intelligence? Should educators be expected to speak correctly?

I have a friend who is working on her Master’s degree and is a college adjunct professor. She has the most atrocious grammar and spelling I have ever heard. I’m talking things like “I seen her” and “that ball gown has sequences on it”.
She is a very bright and knowledgable woman, but this irks me to no end.
I’ve also encountered several teachers (especially elementary) with horrid spelling and grammar.
Am I being too egghead? Can grammar be overlooked in regard to intelligence and competency?