To be fair, this whole thing was heavily forshadowed in the main game proper, she mentions during the femdom session this very scenario (If I had a cock I'd cuck you son), she's shown to have quite the temper at times (something Catherine probably inherited), and during the monkey business futa game she is shown to be petty and vengeful when it comes to minor slights (her force femming the Sterling NPC in the game because he didn't like the food she gave him).
And, like, the two things don't even have to be mutually exclusive, Ophelia can be both a caring mother but also a domineering lover, what tipped everything over the edge was the new hormones in her body turning her in what is essentially a sex criminal assaulting certain women who are clearly not giving her their consent to fuck them until it's too late.