I believe that's better translated as "a lány megy". To proceed is a lot more accurate translation for halad, especially as it doesn't only mean proceeding by movement, but also, for example, proceeding with a project. But since go is one of the hints, maybe you should try reporting, and maybe they'll add it.
Blame English for not having words for certain things :D Anyway, in English we use compound structures for some tenses with auxiliary verbs etc. while Hungarian solves these problems in different ways. E.g. "I will have been waiting for you" (really a monster for foreign speakers!) would go simply "Megvártalak volna" in Hungarian, but the difference is the structure and the general approach to tenses in the two languages.
On the other hand, I've read somewhere that daily used English has the smallest vocabulary among the European languages while Hungarian has one of the largest. But take it as a rumour only, I don't remember the source :D
Never rely on Google Translate, especially don't if you try to cope with Hungarian. GT sometimes translates completely gibberish, other times it suggests just the contrary of the statement, etc. "Girl is walking" means "A lány sétál" or "A lány gyalogol".
Actually "A lány halad" is a very unfortunate example as it has very different meanings in different contexts. It is either express a progress or an advancement, a forward moving (by any means, as it has the focus on the moving itself) or getting ahead. "A fiúnak túl nehéz a magyar, de a lány halad" would mean "Hungarian is too difficult for the boy but the girl is getting ahead". You may get this easier if you remember that "halad" is a smooth movement ahead or forward and it can mean either spatial movement or getting ahead with something. "What about doing the dishes?" "I don't care but the girl does it well" – "Hogy állsz a mosogatással?" "Nem foglalkozom vele, de a lány halad [vele]" etc...