Such an issue is surrogate parenting. To arrive at the correct decision involves applying various Scriptural principles to that specific situation. And without faith it is impossible to please God. I will bless her and will surely give you a son by her. May God Almighty bless you and make you fruitful and increase your numbers until you become a community of peoples.
Children are a blessing which is different than a right.
God, in his wisdom, sometimes chooses to bless some people with children and he withholds that blessing from others. As with all blessings, such as wealth, success and prosperity, God's sharing and withholding of them may not necessarily be liked by us. Nevertheless, Christians should carefully search their heart in the matter of infertility to assure that they are not presuming a blessing to be a right. Such selfishness is a sin. This does not, however, preclude someone from trying to have children when they have been diagnosed infertile.