Hi,

You're at the middle of the bridge:
If you loose the brace then the patient will have problems with her hands while re-tighten the brace.
If she does nothing, she can't sit.

The brutal solution is avoid sitting.
I had a such case and a solution for transcient sitting is to use tall sits that enable a "comfortable" position for meals and reading but increases unfortunately leg fatigue.

The second way is to use a special sit where hip flexion is reduced (exists for PTs).