What delays Isabel's return to Bridwell in Anderson's novel Chains?

It is important to realize Bridwell is the prison where the rebel soldiers are being held in Anderson's novel, Chains. The answer to your question can be found in chapters 38 and 39. Before this point, Isabel brings food and other important items every day to keep the imprisoned soldiers alive. Isabel supports the soldiers because of their brave fight in the Battle of Fort Washington; however, Isabel also supports them because her friend, Curzon, is among the prisoners. Eventually, Curzon becomes very sick. Isabel's visits then become more important than ever. Isabel tries to visit Bridwell every day.

Unfortunately, during the Christmas season, Mrs. Lockton discovers Isabel is aiding the rebel soldiers at the prison. Mrs. Lockton forbids Isabel from helping further. This direct order from her owner is what delays Isabel's return. In order to return to Bridwell, Isabel is forced to spill the water bucket so she can fill it in town. When Sarah allows Isabel to fill it again, Isabel visits Bridwell and disobeys Mrs. Lockton's direct order.