so i killed this annoying woman named Saliah, she was Dawnguard and had some map and key for caches. does killing her make the Dawnguard hostile Torward the dovahkin or is she meaningless to the DG?

She's encountered out in the wilderness without witnesses, so nobody knows what happened.

I'd say that the best thing you can do is go there yourself and see if they attack you. I once helped two vigilants of Stendarr in a fight against some undead. I didn't even hit them once, they got killed, I go over to join the Dawnguard and I get attacked by Agmaer right at the entrance to Dayspring Canyon.