“My daughter is now celebrating 5 years of sobriety. What are the chances she could go back to bad habits?”

First, congratulations for your daughter's happiness and sobriety. The wording used by science is abstinence and learning day-by-day skills for the recovery of wellness. This needs not only to abstain from abusing a substance, but from all addictive substances (including alcohol, marijuana, addictive pills), and also learning each day problem solving skills that results in gradual changes to a more healthy lifestyle. Support networks are important in this day-by-day process of finding new, healthy friends, activities and to recover our love for life and to serve others. Very probably your daughter is doing all this process because it is probably causal for her sustained abstinence and happiness. The danger of relapse is always there, but may be minimized maintaining support networks like 12-step groups; maintaining therapy if the person has other concurrent mental illness and minimizing contact with dangerous situations that may result in craving and managing stressful situations. During severely stressful situations, the early consult with a sponsor, therapist, or a councilor with minimize the risk of relapse.
Thanks.

Roughly less than 15%. She is on the right track. Keep her involved in recovery which will reinforce accountability.

Addiction is a chronic medical disorder, like hypertension or diabetes. Thus, while in remission with your daughter, congratulations to her, it can have a recurrence.
Things to “watch for”- her triggers
such as old places, people or things she associated with her using.
Frequently all of us revert to our former, well known coping tools, even when self sabotaging, if we are stressed or overwhelmed. Thus, I would suggest watch and support her functional behaviors and lifestyle tools.
If she begins to isolate, returns to old behaviors,
contacting former playmates( users) and/or returns to former playgrounds ( places where she obtained or used) those are major cues to risk for her to be overwhelmed and/or stressed and falling back on her known methods of coping ( self medicating)

Try to remain non judgmental, require honesty and accountability of her. Be supportive and always willing to communicate openly and honestly with her.
Responsibility and accountability are keystones to her recovery.

Serenity, Courage, Wisdom- Doc Soper