Let's suppose a version of Dr Walsh who was formerly affiliated with the Council, and parted ways with them because they weren't interested in pursuing her new and modern research projects about "what if we could get more Slayers?"

Let's also suppose the Slayer line is still with Buffy. Kendra was called when Buffy flatlined, but since Buffy didn't stay dead, Kendra's death doesn't call anyone new.

So Walsh is setting up her project in the US, and the Watcher monitoring Boston-area potentials is still an ally of hers, and so she takes Faith Lehane, whom nobody will miss very much, and puts her in the super-soldier procedure Slayer awakening procedure. This does require a vampire to "donate" its power, but luckily her field team has captured Angelus, fresh out of hell and very confused. (We might say here that he returned to Earth in late summer, when Buffy was still being very miserable in LA.)

The procedure has machines and modern restraints and a lot of technical terminology, instead of chains and three magic dudes with their magic sticks, but it's still basically the same process; get hold of the demon, twist it up just right, and infuse it into the girl. And the result is Faith the Vampire Slayer.

Walsh has a handful of soldiers on loan, to help Faith train and get used to her new strength, under the guidance of that Watcher from before. And then she goes out for the field test, and things go very badly wrong when she gets the attention of Kakistos. And season 3's plot unfolds from there, except of course there's no Angel in Sunnydale. But when Spike comes to town, he thinks there must be, because his demon can sense Angel's demon in town…

(Bonus points if Walsh still tries to set up shop in Sunnydale, and Spike has to escape from her facility and is like "listen to me, they've got girls in there and they've got vampires, and i don't know what they're doing but it's Not Good".)