Answer: Breed for black-haired pigs
Explanation:
Now according to the statement, the farmer catches wild pigs and mostly are brown.
Since black hair is dominant over brown and also black and brown are dominant over red, this implies that red is the least dominant color meaning if breeding occurs, there would be less chance of getting red colored pigs.
She wants to breed either black or red haired pigs and since black is more dominant so she should breed the black ones with the brown ones or with themselves so she would eventually get pure-breeding herd i.e. of black color.