Well, after talking to the vet, seems the best thing to make Kerry and Sasha blend nicely is to take a trip to the behaviorist/trainer.
Got an appointment next month and spoke to her breifly. Seems it's pretty common stuff. Normal terrier uber-bossiness combined with the sensitivity and easy spooking of kerry blues.
She thinks it's all fixable though--even though made harder by the fact the dog's unable to be crate trained (major freak out--you should see what she did to the back of the station wagon).
So soon, hopefully, we'll be able to successfully get her to stop:
-shoving the baby
-herding the baby
-snapping at the baby (turns out it wasn't a one time thing)
-snatching toys, cups, etc. from the baby
...and so on.
Seems in bossy or easily spooked breeds that it's fairly common for this to happen when theres a newly crawling or walking kid--depending on when they are eye-level or taller with the dog.
No one tells you this stuff. Sure, they all go on about bringing home a new infant to dogs.
That's the easy part.