Aircraft structures are designed to withstand a specified load with a very small safety margin.

That safety margin is 1.5.

The question states that the aircraft is stressed to -1.9 to + 3.8g.

The turbulence has stressed the aircraft to +4.2g.

This exceeds the limit of 3.8 but has not exceeded the ultimate limit (3.8 x 1.5 = 5.7g)

The structure will therefore not fail but be permanently damaged.