I think there are many ethical ways to terminate. Many reasons for one to leave their job

If she decides not to return to work to care for her children full time, or if she all together quits her job, change her career path, goes back to school, if she moves out of the area, if her family needs her, heck if she develops health problem or becomes independently wealthy or need a better paid job because she becomes a single parent.

No one can force anyone to work forever even in the caring career path.

She does need to offer resources and send referrals. But she can’t be obligated to maintain her clients for life. I know it’s hard to accept that it’s a job, not just a relationship.

She’s not trapped because working this job is her choice. But she could make a different choice. It’s not against the law as long as it’s done properly