A confirmatory PCR is not necessary unless your employee develops symptoms.
You should allow your employee to continue to work from home during self-isolation. If working from home is not possible, you should treat the period of absence from work as paid sick leave.
Your employee will end their self-isolation after they get an ART-negative result.
You should exercise compassion and flexibility in supporting the needs of your employees.
Every employee who has at least 3 months of service is entitled to up to 60 days of paid sick leave, including hospitalisation leave, which should generally be sufficient to cover self-isolation.