I've heard people say that they had trouble with that fight on normal but Abigail at least stands up there after 20 seconds to heal you, when you lose Abigail on hard she's down for good and I couldn't see any way of keeping her alive either.
It wasn't THAT bad for me. If you position yourself well at the start of the fight (to protect the damn witch), and manage to kill the first few barghests quickly,
The Beast and the dogs it summons will focus on attacking you, and the witch will help you (she sometimes casts some sort of healing on you). Then just use Group style to fend off the mutts and strike the big bastard with Aard repeatedly.
If you're using the specter oil and some potions (Tawny Owl, Swallow, maybe Blizzard?), you should manage to survive long enough for one of your Aard attacks to succeed, and when the Beast drops to the ground you can just jump in and finish it like any other creature.
I had to repeat the fight 3-4 times to get it right, but it was OK - just enough to be challenging, not enough to make me throw the PC out the window