Thats terrible, I lived thru a love story like that for a year, but eventually drew a line to protect myself. With a sister it must be different again.
The medication is bad, makes it worse in my opinion.
Big Pharma never healed anybody bipolar, patients gotta take the shit for the rest of their lives, or go nuts even faster without it. Must be awful to be on Lithium every day, with all that side effects and change of personality.
There are a lot of new publications lately. Diet and sports are essential, nature, change of habits, clean conscious lifestyle.
Psychedelics are said to work very well. But probably hard to find a clinic in the UK going for that, and could become a bit adventurous if done at home.