This is a show where the protagonists are not just
anti-heroes, but outright villains. After their murders of innocents,
blackmail, and the cruel con games played on Marta and Annalise, it's so
peculiar that sleeping with an underage girl is where the show draws
the line. Apparently statutory rape is worse than murder.

She endangering the SA mission, but advancing the mission of recruiting her daughter. Elizabeth might find that tradeoff worthwhile. As for kids being valuable parts of covert ops, I'm sure you can find many examples in real world history, starting with WWII

The KGB doesn't control how Elizabeth & Philip conduct their ops, they can choose their own modus operandi. Now, is endangering her daughter something that Elizabeth would do? Yes, as demonstrated in that flashback where she threw 5 year old Paige into the deep end of the pool.

Prediction: Elizabeth will use Paige as an operative in the anti-South African operation, while keeping her in the dark that she's actually working for the KGB, since striking against apartheid is something that liberal Paige can support. During the op, Paige will be force to commit an illegal and/or immoral act for…