A good percentage of people who need therapy only get it after repeatedly failing at things everyone around them can do. (Especially developmentally disabled children). This is often humiliating.
This means that therapy can be triggering. Therapy involves focusing on difficulties that someone has learned to regard as humiliating flaws. It’s important to keep this in mind when you give therapy.
Don’t expect someone to trust you right away. You have to demonstrate that you are trustworthy. You have to show them that you can be relied on to treat them respectfully. You have to demonstrate that you won’t ever regard them as broken, or make respecting them contingent on them progressing toward a cure.
And it needs to be true. You can’t just affect safety and kindness. You have to actually be trustworthy in a deep way, and let that show through your action.
You don’t get to decide when you have established trust; you don’t get to decide when someone receiving therapy should feel safe. It’s up to the person getting the therapy. (Even if they are a child.)
And if you understand this, you’ll be much more able to help people.