Friend, your beloved sister shall rest in the glory of God’s mercy, regardless of her fate. He is always wise in judgment and merciful in dealings. Never, ever forget that as you pray for your dear sibling!
Just remember that the Holy Church which God founded upon Peter’s brow has dogmatically defined mortal sin for us. The action must be grave/serious, the actor must have full knowledge of its gravity, and there must be full consent on the person’s part. Now, look at the intensity of bi-polar disorder and tell me there is full consent, or even full knowledge of cognizant actions at times. You can’t tell me that there is full consent for some actions taken while manic or depressive state! There is always hope, for she was a tortured soul, but now all tears are wiped away by the breath of the Holy Ghost upon her being.
My apologies if I sound too scholastic or scientific in classifying your sister, but we must be precise. God is merciful, and His actions in history can be seen and recorded for all to see. If His grace preserved the Blessed Virgin from all sin before birth, His grace can fill your sister for eternity.
Requiem aeternam dona eis Domine, et lux perpetua luceat eis