And how would Mercy react when she find out who the mother is?

itshigh-boop:

She’s heard of the entity “Sombra” responsible for global hacking sprees but she really didn’t know it was actually one woman. The fact that McCree has grown close to someone who frequently skirts the veil of morally right and wrong choices, isn’t really that surprising to Mercy. But the fact that he’d grown close enough to have a child with the hacker…that was something else.

She might chastise McCree for being careless and she’s in no rush to meet or befriend Rose’s mother, but she bears no ill-will toward the girl. Rose is a well-mannered, polite, healthy, and overall happy girl. McCree insists that both he and Sombra are involved in raising Rose, so at the very least, Mercy can respect that Sombra is being a responsible mother.