My 7yo daughter is totally hooked on Mighty Math. Standing in line (zoo, store, whatever), other kids are almost cartoonishly leaning over her shoulder to play

My 7yo daughter is totally hooked on Mighty Math. Standing in line (zoo, store, whatever), other kids are almost cartoonishly leaning over her shoulder to play along. It may be evil, but the realy game changer was when I started experimenting with paying her for right answers: $1.00 for ten out of ten right the first time, $.25 for 7 out of ten right the first time, or $.01 for each one right less than 7. Am I destroying my child's humanity through pay-for-performance? If so, how?