Do you mean she speaks English with a pronounced accent or that her grammar and vocabulary are poor?
I speak Spanish, with no English accent. So much so that I have been asked what part of Mexico I was from. However, my vocabulary and grammar are not nearly as good. I knew a gentleman many years ago that was nearly perfect in grammar and vocabulary, he even preached in Spanish, but his accent, his pronunciation was terrible. He lived and worked among Mexicans for over 60 years and it never improved.
So I can believe that our First Lady speaks many languages, she just may not have the ability to mimic the different sounds that are made in different languages.
grammar, vocab and enunciation are all poor. I wouldn’t even mention it, if her spokespeople didn’t constantly bring up her being a polyglot lol