An easy GDP growth question
You are confusing money supply with GDP. GDP is defined as the total monetary value of all goods and services produced within the economy. For this case,

GDP =  Woman's Earning + Gardeners Earning

Before Marriage = 1000 + 60 = $1060 


Even though the woman has $940 she was still compensated $1000 for whatever service she provided. The money supply is 1000 but GDP is not.

Post Marriage = 1000 + 0 = $1000