I reckon she looked thrilled that the baby will most likely be a boy, proudly stating the baby feeling like a boy
They already had a boy so killing the unborn 'son' is not going to stop anything and nowhere It’s hinted at that Mike knows Anthony isn’t interested or a fit for that job Where?

As per their conversation, Anthony had taken his place, wanting to help Michael as of now not wait for someday

"legitimacy" was difficult not impossible
As we most recently debated in Did Roth sort of win? thread he had achieved the semblance of legitimacy and as We see in GFIII more "legitimate" than ever

She wants the unholy and evil Sicilian thing to stop by being unholy and evil herself, killing an innocent unborn child to spite her husband and the child's father Nice!

She was a prisoner couldn't even go to the market
If medical check ups "Who the heck is going to abort Michael Corleone's child?"
It is implausible Pete but no doubt made an emotional ladder that still gets pulled out from under all of us