What are the requirements for South Africans transiting through Thailand and picking up luggage?

If she booked 2 separate tickets hence South Africa-BKK and needs to check in for BKK-Cambodia then she needs to go through Immigration and do all requirements for entering Thailand.

Best firstly to check with booking agent or airline, plus Cambodian requirements for entering on sealed air-routes.

If she needs to go through Immigration to pick up her luggage I could imagine its meaning Thai Pass, Test & Go scheme (which is 6 days stay in Thailand but maybe 1 day Quarantaine hotel in this case??), PCRs tests, insurance etc

She most likely needs a sealed route to fly to Cambodia, might be cheaper and less time consuming to cancel and book another flight.

Live in Thailand. Haven't left for 2- years to border countries due to fluctuations in immigration.

Find a place to lite and wait it out.

Which airlines is she using?

Many people book separate flights on separate tickets. And then you have to go through immigration to pickup your luggage and check in for the next flight.

The OP mentioned in his question that she has to pickup her luggage in Bangkok .....

Ask the airlines. Passengers never go through immigration on a transit flight nor leave the airport. Ask them.

Was originally told my covid test results would be 4 hours. Got results 10 hours later 😆

She needs one ticket to be able to transit.

She will need to enter Thailand, so she's not a transit passenger. She will have to apply for a Thailand Pass. Assuming she's fully vaxxed, she can do Test & Go, but will need one night in a SHA+ hotel.

To be able to pick up the luggage you have to pass immigration. She needs a Thai Pass , Test and Go, and the flight to Cambodia shouldn't be earlier than 24 hours after arriving in Bangkok.