obtaining child custody after taken away by courts

A friend of mine has been through some really hard times the last several years. Among her problems are losing custody of her 5 year old son to her ex mother-in-law. The court deemed this to be in the best interest of the child. She fell into a downward spiral with substance abuse and has since gotten into more legal trouble including PI and failure to appear. Is it possible, if she can show dramatic improvement and completion of therapy with continued meetings, she might be able to regain custody? The criteria in which the courts judge these things seemed stacked against her. Would losing her child be a legitimate factor in explaining such behavior? Please let me know what can be done, if anything, to reunite a loving mother with her son.