I'm in a similar position...
My mom started chemo earlier this year, (completed her treatment two weeks ago) and then her mind just suddenly deteriorated.
She went from normal forgetful (67 yr) old mommy to belligerent, verbally abusive, delusional, stuck in time loops mom, after just 2 months.
I was so ill prepared, its just not funny.
It hurt alot at first, being the main target of her vitriol. It was also quite shocking to hear my mother use swear words for the first time in my life... My older siblings didn't take me seriously at first because they never saw that side of her in the beginning.
My T at the time helped me alot to process her anger and manage how I reacted... I'm an emotional sponge so I ended up mirroring her moods alot at first. It was very draining.
Everything is a battle, she never wants to take her meds (I'm either drugging her, trying to kill her, or turn her into a junkie) refuses to wash, and hoards anything she can find, even candy wrappers if you don't watch her... She's also under the impression she is able to be self sufficient, but she reheats her meal and then forgets what she's doing mid way, then still asks you who's food it is... She also loses track of time and once swept the yard for three hours!!
Of course she argued that she didn't and I was just trying to convince her that she is going crazy.
I don't really have any sage advice, I just wanted you to know I get it, PM if you ever wanna chat, we can whine to each other