Yes, I would guess this is for dominance, but not in the usual way. Since she is only 12 wks, I would say this is more testing the waters kind of dominance. She is around the age where she will be testing to see what she can get away with, especially with Kiah.
I would put a stop to it if Kiah doesn't on her own. Unless of course it doesn't bother you. Gunther tried to do that a couple of times to Keiko as well, but he never actually humped "on" her, more like he stood next to her and did it. He was smart b/c she would have let him have it if he ever did try getting on her.
With Gunther, this phase only lasted a short while (like b/t 3-5 months), b/c I wouldn't let him hump anything. Like I said he tried a couple of times with Keiko, once with me, and a few times at the dog park with some friends. Of course Gunther is a submissive, so that does make a difference. If Kitana is more of a dominant or alpha type, she may try to get away with it more often.