It's not a big deal. Nina's not a big deal. But she is deceitful She wants a baby with a man who told her he's in love with someone else and she is willing to drug him and give him no choice. She wanted to get rid of Rafe for her own protection, she wasn't being kind or generous. Silas cheated, yes he's a douche but he doesn't deserve to be raped. IMO that's what it would be if she drugs him to get pregnant. Does she even know if she's still fertile? I FF a lot of her so IDK if she realizes she's almost 50 years old, physically. It's a soap so that doesn't really matter, I guess.
If it's not a big deal to her, why wouldn't she tell them? As a schemer, I find her pretty ineffectual. Lucky but ineffectual.