Can you give some examples?
The only situation even close to what you describe, that I can think of, is Tamar, who seduced her father-in-law, Judah, and conceived Perez, an ancestor of David. And I don't recall anything about "good hearts" or "motives of love." The story in Genesis takes the position that she was justified because Judah had broken custom by not allowing her to marry his youngest son.
Lot's daughters thought the world was ended, and slept with him.
Jacob's wives gave their servants to Jacob to get more children (servants kids were considered their own). And Abraham's wife also gave her servant to her husband to have a child.
All of these things, like Tamar, are considered "justified"...but nevertheless, all were pretty shady business...that's the point.
And I know many women who have "replacement babies" to replace the ones they aborted when they were too young to know better, or when they were pressured by parents or boyfriend to abort. Babies are the way to heal this wound...
I agree, it would have been better to adopt, or to care for children in a differnt way. But I pray she has her heart healed by this child...