Regaining trust takes time. Often a long time. Generally, you can:

• communicate often and be specific about things; create expectations and then deliver
• accept that she has a right to be angry and mistrustful, don’t be resentful
• avoid even the appearance of wrongdoing
• ask and be considerate of their feelings; if they are uncomfortable with you doing something don’t do it even if it seems unfair or silly

They are sort of mourning the loss of the person they thought you were, and don’t be surprised by grief or rage, but it should become less over time.

Good luck.