I believe that at 7 weeks she can't identify where a sound is coming from very well (maybe not at all?). That skill takes some time to come in.

She is also unable to think about a couple of things at once. No multitasking at all!

So if she's concentrating on something in one direction and you speak to her from the other direction, she really doesn't realise that you are talking to her, or where you actually are. This has nothing to do with her hearing, everything to do with her brain development.

If you are interested, there is a book called The Wonder Weeks that is about brain development in babies, and also about when to expect and how to deal with the inevitable fussy stages and the times when baby is learning lots of new things very fast. It's a good read, not difficult, and really really interesting, if you are into that kind of thing. It has a lot of discussion about what things to expect your baby to be doing at different stages, as her brain develops new abilities.