Hi Polina,
Granmatically, putting the complement starting with 为了 after the main clause does make sense, but you wouldn't really hear it being said. So we'd prefer 为了xxx,xxx。比如:为了她的儿子,她每天努力赚钱。Alternatively, we could add the 为了。。clause at the end of the sentence, if we add another phrase to emphasize it. For example, 妹妹天天来我家,就是为了来吃饭, or 我逛了一天街,只是为了找一条裙子。It sounds better when we have "就是为了” or "只是为了”instead of "为了” when the complement comes after the main one.