Upvote:1
Brazilian citizens are visa-free for short visits to the Schengen area, but only for short visits.
In order to be allowed to enter without a visa, your girlfriend needs to actually have plans for a short visit, all of it, including when and how she's going to go back -- and be prepared to document those plans. The fact (?) that Germany may allow her to change her plans during that short visit and apply for a long-stay visit does not affect that.
After all, even though the authorities might entertain a long-stay application from your girlfriend during the short visit, it is not certain that they would grant it, and at entry the border guard needs to be convinced that if the application is denied, she would actually leave at the end of her proposed short visit.