Even though Prince Brand has been nothing but kind to her in his own way, Starwind assumes his intentions are bad:
And what if this is all stuff and nonsense and Brand's dragged us here for some other reason? Then you'll have just given Brand a chance to--I don't know what he'd do, but I'm sure it wouldn't be good-- and all for nothing!
She's not sure she trusts a word Brand says:
I think that someone, or several someones, are not telling us the whole truth; but I don't think we've had the entire truth about anything to do with Amber since we first met in the Horn and Hound.
Her distrust for Brand is pure instinct; it doesn't have anything to do with any solid evidence she has against him.
and then there's the Avenging Angel, and what Fisher read about it, which we still don't have an answer for, except that it tells me that my bones are right when they scream at me not to trust that kindly old man Prince Brand.