Kay was one p***ed-off woman.
Her having an abortion was a deliberate rejection of Michael and everything he represented to her.

I know Ultrasound has been around for a while but were people using it for sex determination in the fifties? Not sure.

Anyway it's a great scene because you see how angry and vindictive Michael and Kay can become when pushed to the limit. She tells him about the abortion and mentions this "Sicilian thing" specifically to hurt him as much as she can.

I think Vincent was exactly the sort of person that Kay had in mind.

"When the snows fall and the white winds blow, the lone wolf dies but the pack survives."
Winter is Coming

Now this is the Law of the Jungle—as old and as true as the sky; And the wolf that shall keep it may prosper, but the wolf that shall break it must die.
As the creeper that girdles the tree-trunk, the Law runneth forward and back; For the strength of the Pack is the Wolf, and the strength of the Wolf is the Pack.