Man this fight solo is... Something else. Running out of stamina is a real issue - they never stop attacking. You need to be super SUPER patient and wait for openings to get one or two (if you're lucky) hits in on the blade bearer before returning to spamming the dodge roll because these ****ers NEVER STOP ATTACKING. Seriously they saw duo fights in Dark Souls III, Friede and Father Ariendal, the demons from below, and implemented it poorly because they don't understand what makes a duo fight good. Attacks from offscreen need to be telegraphed (Friede's floor ice in phase 2, the demon's explody breath) and there needs to be a cadence to the fight with breaks where you can do your damage. This fight fails on these fronts, the two opponents have AI that just says "attack constantly", the canoneer has attacks that blast you with no telegraph, the blade bearer gives you no room and closes distance shooting up your *** faster than a crucible knight. **** this fight. It could have been good too, imo, if they just toned down the aggression a little bit and had something like a laser sight from the canoneer for his fireball attack so it can't just blast you from offscreen with no warning.

honestly, all the guides out there (even here) try to say to attack cannoneer first. this is horse-crap imo. he is the slowest, and easiest to predict out of your peripheral. he also is a meaty boi, so time spent trying to whittle him down is time for blade bearer to do the real hurting. best to go in with fire lily/blazing roar/flame spike/etc set on a high mind/will build, any spell that can hit her despite her speed and with a quick cast animation. she will melt long before you die to cannoneer. also, in my experience at least, she REALLY loves to chase you over any partner you have, so its like the game is tryin to tell ya to deal with her first anyways. oh, and this should go without saying but despite it making you more frail, i would suggest a build with quick dodge, you DONT want to be caught off-guard by fat rolling lol

I didn't even like these two back when they were Ornstein and Smough.

The whole battle is just Devs be like "we know the game may be on the easy side, lets change it up". Pretty easy if you can imbue your weapon with fire.

who knew nicki minaj would be this good with a sword?

I play frost spellblade build (Artemis Blood code, willpower and dex focused) with Yakumo as companion. I struggled with her untill I swapped ice gifts for fire ones. It was a bit easier, but still struggled.
Point is - in your first NG, you won't outrun her as much as you would might think (at least with my build I didnt). Yakumo is a good choice, because he's a meatshield, and he won't die as easily as Mia or Louis.

I've tried Louis as my partner (since he attacks mainly with fire Gifts, and I was ice spellblade) but even with his communal gift, it was Yakumo that really made the difference for me.

On my second character I've tried poisonong her. It was a good move.

Updated Status Weaknesses as of 11/5/2020:

Both Cannoneer and Blade Bearer are susceptible to venom, inhibit, slow, and stun.

I'm proud of you Ornstein, finally having the operation. Now you can finally be the beautiful woman you always were.

Short Answer: Bring an AI partner and use BLOCK. If you have "guard reversal", a high-block weapon, and a functioning block button, she will take minutes to kill you. With a high block build you can stare her in the face and take manageable damage, and doing this with guard reversal will stager her out of her combos. This is MUCH more reliable than trying to dodge her fast, darting combos.

After farming the twin bosses depths, it seems that killing Cannoneer first is the best as long as you can block and heal.

Was stuck on this for quite a bit until I realized that Flame Weapon from the Prometheus code literally just shreds the ice *****. Didn't really need anything else apart from that, she died super quick and the flame fatty is just free afterwards.