She takes off the coat would be "ela tira o casaco". So, "deixa" really means "leave"

Probably just an oversight, I think the Portuguese course isn't quite as thoroughly developed as some of the other courses that have more users. If they give it as a hover-over hint, it makes sense to be consistent to either accept it, or remove that hint. I'd report it whenever you encounter anything like this. Ideally if they're not going to accept it, I wouldn't want it given as a hint either.

I guess you could use it in the context of, "She leaves her coat at her friend's house" or something like that.