Q.Bonsai Jade Tree
Can I save my jade (I call her Mary)? I noticed little leaves dropping and was told to submerge in water 1 min, drain and put back on stand. Then water when soil is dry. I did that but it rapidly lost all leaves, parts of the tree {bark} is light color and other part is very dark. I took it out of ground to look at roots. They are dark but strong to base, which has a light color but parts of branches are dark and some look wilted on tree. Yet, the tree looks dead, like a tree you would see in the winter. Was told in summer to transplant with soil.

Healthy roots on a jade are white and firm. Dark roots are not healthy and are usually caused by root rot - which would also cause your leaves to drop. If all your roots are dark in color (which it sounds like they are), I am afraid that the prognosis for your jade is not good and that it is probably irrecoverable.
For more information on the care of jade plants, please visit the following link:
https://www.gardeningknowhow.com/houseplants/jade-plant/jade-plant-care.htm