Shrewsbury School graduate Wong, who was first involved with England's academy in 2019, was a reserve for the squad in Taunton but replaces Central Sparks team-mate Emily Arlott, who is recovering from Covid-19.
Uncapped pace bowler Wong, 20, has been impressing onlookers with her form at club level.
She is part of the squad of 13, including heavyweights skipper Heather Knight, vice-captain Nat Sciver and Tammy Beaumont.
Action in the four-day one-off Test began at 11am in Somerset today to kickstart a series of meetings with tourists South Africa.
Following the Test, three ODIs take place from July 11. Fans can take in the action at numerous venues around the country.
The nations then face off in three T20 clashes between July 21-25.
They have also been drawn together in Commonwealth Games group stage action in four-team T20 action that also features Sri Lanka and New Zealand.
England begin on Saturday, July 30 against Sri Lanka at Edgbaston.