Here in the U.S., I believe that it is usual to solo after 8-12 hours of dual. I don't know what the South African rules/laws are about hours required to solo, but 20+ hours of dual seems a lot to me. Long ago and far away, I soloed at just under 8 hours dual. Back during the Vietnam Era, U.S. military pilot trainees usually soloed at around 8 hours and were in danger of washing out of the program if they had not soloed after 12 hours of dual ... at least that's how I recall it.
Whatever happened here, it was an incredible tragedy for the young lady and her family. I just can't imagine. R.I.P.
Regards,
Grog