I literally just did this fight just now. I used nothing but odachi. When she's summoning the ice spikes, just sprint left or right while locked on. They'll fly by without hitting. Play with Low Stance because dodging is super quick and easy. Bait out her attacks and dodge as necessary. Hit her while she's still finishing attack animations after an attack misses. Only hit 1-3 times depending on your weapon speed.
Contrary to the guide and some comments here, Arrows did nothing, so don't rely on those. They can chip at her Ki well enough, but you can just do the above and not worry about it. She'll kill out your Guardian Spirit buff really quick if you let her, but even if you've used it, just dodge the attack coming and then spam attacks on her. If you have enough damage output, she'll die before she can get another attack out as your Guardian Buff ends.