My strategy became to keep relatively close, backing off to heal and waiting for her to do her big swipe attacks, dodging to the side the attack was coming from. I'd then get a charged R2 on her legs with the Saw Cleaver, often making her yelp in pain (a kind of soft-stun that doesn't allow visceral attacks.) The last attempt I made didn't even require any anti-healing.
Having dispatched the massive antlered-werewolf-lady in charge of the Healing Church, I turned my attention to Hemwick.
Now I admittedly grinded a couple of levels (mainly while farming Blood Vials in Central Yharnam, so not a ton of levels) in the fight against Amelia. But holy crap did Hemwick seem like a step down in difficulty. The ladies there do hit pretty darn hard, but a quick thrust-slash combo with the Kirkhammer (in sword form) pretty much takes them out. There are also some not-terribly-subtle shortcuts to open in the area. In fact, the part that felt the most dangerous was actually still in Cathedral Ward, before getting to the Hemwick Charnel Lane lantern.
The Witch of Hemwick is the only boss in the game so far (and probably altogether) that I one-shot. Admittedly, the Witch is probably more of a puzzle boss, and having looked things up ahead of time (with Soulsborne, I have no shame looking for help,) I knew her deal.
Basically, she summons some slow-moving beast-men that you can really just run past. You simply have to search the four corners of the room, the area under the broken bridge and the top of the broken bridge, and she's very easy to get a backstab-visceral attack against. She does have a cleaver which she'll combo-attack with, but I didn't experience any other direct threats from her.
At about halfway, she'll summon a clone, and you can tell which one you're damaging by whether the boss meter is going down. Once one Witch is down, the other will begin resurrecting her, but you'll have a pretty big window, and as long as the living witch is at about a quarter of her health (she was for me,) you can probably make it. Just avoid the summoned beast-men and hunt down the Witch and you're good.
So from here I think I can technically go to Byrgenwerth (I think technically I could have post Amelia,) but I figure this is probably a good time to go try to take down Darkbeast Paarl and explore more of the Hypogean Gaol area.