I don't trust her to have my back. I don't trust her to get results. I don't trust her to do what I want her to do when I need her to do it. I have to have a reason to trust her. I can't just scope by having her trust me. Leadership is a two way street. Her philosophy and outlook will likely inhibit the desired end state I want.
See now we're getting into how you feel about Ashley. Loyalty and trust while not mutually exclusive are two different entities. I don't have to trust someone for them to be loyal to me and vice versa.
Now you could argue about how the level of distrust can effect loyalty. If you are vocal with your distrust of someone then yes their loyaly will decline. If you're discreet however you can still keep someones loyalty while.keeping you distance.
Now my opinion of Ashley is diffrent then yours as I am probably one of the biggest Ashley marks there is (don't know if mark is really used outside of the wrestling community,but what the hell) and you have a clear distaste for the character. We will never agree on how must Shepard trusts Ashley, but we can at least respect each others opinion on the matter.