You are right in saying that laxatives should not be continued indefinitely but polyethylene glycol PEG being osmotic laxative that softens stool and adds to bulk is relatively speaking quite safe.
Your friend can always start taking isapgul fibre as well, and gradually decrease the dose of PEG and eventually stop it.
Health Tips
It is important to consume sufficient amount of water when taking fibre supplements like isapgul.
Avoidance of constipation is a must to prevent anal fissure from recurring