Hi Charithea
Certainly neither S namaensis nor semiatrata. Could well be S argentea. S namaensis has the tiniest little, crinkly, green leaves. I got a few seeds of S semiatrata to germinate but the last of them died a few weeks ago. But the rosette you show doesn't look like the photos I have seen of S semiatrata. I am contemplating buying an established plant of S semiatrata this weekend because I was only partially successful with the seeds.
I wrote earlier on this thread about killing off my S clevelandii by watering it in summer. This year I have a second plant and I have left it in a pot . I moved it out of the torrential rains we had just recently so it has had zero water since the late spring. Still looks okay. Now I am panic stricken about starting to re-water it. I will let the weather cool a little more first I think. But it could be a plant for you to consider for your long dry summers. The scent from the leaves is amazing. They say that the native Americans say of the plant "First you smell it, then you see it". It is absolutely true. The plant I had last year, a mere cutting that had grown a little over the winter, filled my small garden with perfume. Light and fresh, though. I don't think I will ever be without one again. Don't judge the plant on the photo of my cutting. Have a look at the real thing on the internet.