Won't convert ticket to a voucher when family member tested positive for COVID

My mum who is over 60 years booked a flight to JHB to DUR on Kulula and return with FLYSAFAIR for this weekend to attend a function. We were informed last night that a few people in that household tested positive for Covid and therefore the function is cancelled. I contacted Flysafair immediately to find out if the booking can be transferred to a voucher as my mum cannot risk her life and travel. Flysafair referred me to their refunds and cancellation policy (which is not aligned to Covid), and tells me that my mum can go to the Dr and get a letter saying she is unfit to travel to get a 50% refund or make changes to the booking, which I'm not sure how we can make changes yet, if we don't know which future date to book this for or cancel the booking to a voucher and get R300 deducted as an admin fee. I tried explaining that these are not normal circumstances and we don't have a choice, we don't want the money back, and only asking for it to be transferred to a voucher so that she can book and travel when it is safe again. Kulula managed to understand this and put my mums ticket on hold for 6 months, whereby she can rebook, why can't flysafair do the same and understand the situation??