There are probably multiple reproductive strategies out there in the population at large. Heck, we each probably have multiple strategies encoded in our genes that get activated depending on what kind of opportunities and obstacles we find in our environments.
Interestingly, this particular lady supposedly had another 3 children after selling her first 5. If her behavior was a result of genetics, those genes were pretty successful.
To be pedantic, the success of this strategy is probably frequency dependent (which is common, see the classic hawks vs. doves game theory literature). That is, it is more successful the rarer it is, but less successful the more common it becomes (because the people buying your children are more likely to be callous and treat them as slaves, rather than as adopted children), eventually settling on some stable ratio in the population.
Interestingly, this particular lady supposedly had another 3 children after selling her first 5. If her behavior was a result of genetics, those genes were pretty successful.