Addiction is a chronic, often relapsing illness, like many other illnesses.
When someone relapses, this does not mean she's failing in recovery, or not motivated to recover, it just means you're made a mistake, one you can learn to avoid with greater awareness. A tendency to relapse is a natural part of addictive disease, in other words, and even people who are highly motivated and sincere about their recovery can slip. So it follows that if someone relapses, he or she should be allowed to receive more treatment.