This is a little subtle. The sentence is telling you a story. As you know, a story can be told "in real time" meaning that the reader is hearing the story as it happens - so the reader places himself mentally at the beginning of the time period that the story occurs in, and prepares to follow its development in step with the characters involved. OR the story could have all taken place before the reader learns of it, so it is all recounted in the past - so the reader mentally places himself at the end of the tale, as if he is hearing about it from a raconteur at an inn. And then here's the most interesting one: the story could have started before the reader learns of it, but is still going on. So the reader has to mentally place himself somewhere in the middle of the story, and be prepared for flashbacks, etc. You see this in movies a lot.
In the first sentence, the use of the word "has" in "the teacher HAS asked her" causes you, the reader, to understand that this request already occurred, BUT - it ALSO IMPLIES that the story is not over yet - that there's something else coming. This tense puts you somewhere in the MIDDLE of the story...if you see what I mean.
By contrast, "the teacher asked her" is entirely in the past. From reading this little snippet only, you - the reader - would assume you should mentally place yourself at the end of the tale, and expect that everything you are going to read will have already happened.
("will have already happened"...how's THAT for a tense?)