Yeah even with the DLC she is by far the hardest boss, even if you summon pals. She requires specific approaches, good reads, and fast timing to take down.
If you are a tanky guy and want to solo her (or at least just use ash and no player help), the fingerprint shield is a must. For a weapon in this scenario, any reasonably fast spear with Blood Tax on it will fuck her over pretty good. Look for openings to counterpoke her too. If you got the Pig Rider guy's spear from the DLC, that is the optimim weapon because it both provides massive bleed scaling and the moveset is the easiest for counterpoking her out of some attack sequences and its jump attack will even sometimes knock her out of Waterfowl during startup. Toss in the mimic with the heal flesh on your hotbar and the fight goes from unforgiving to relatively manageable, since you can back off to heal if you need to.
You can do the dex route and learn to parry on top of that, but that requires perfect reads and reflexes. I was never able to solo her like this, but I can recommend getting some throwing knives to cancel her waterfowl windup. Do NOT call in an ash if you go this route, because all you are doing is feeding her healing.
Being a caster against her is basically nearly impossible solo with or without an ash summon. But if you just want the kill and are doing coop, being a caster is a great way to do some damage and not fuck it up for the other player by making her agro hop more. Night Commet, the homing back fireball INT/FTH spell, and the big bow spells are all solid choices if you can maintain distance. If you have enough arcane, cloud of flies spam is great for stun locking her and building up bleed for your allies to capitalize on. Also note that the bulk of her room has watery areas so any lightning spell or incant without direct targetting (so she just dodges) is going to perform decently too. Gransax Spear is actually one of the best weapons to use on her in coop due to the weapon art and being able to use the shield counterpoke strat.