Care for sister?

I have not talked about my youngest sister...I am the oldest of four girls my parents have. My youngest sister has microcephaly and just recently diagnosed with Parkinson's disease. The microcephaly caused her to be mentally disabled, retarded, intellectually disabled, or whatever you want to call it. Her brain and skull do not grow at a normal rate, thus her small head. The Parkinson's has been hard on my whole family, but my mom the most. I have always been connected to sister, since I was able to understand she is different from me. I remember thinking if only she could have my brain! I know too sacrificial but I was 9 years old and although she is different she is amazing!! I love her so much and can not imagine my life without her!!!
Now she is 20 years old and very dependent on my mom/others to care for her. She once had energy to dance and sing to Selena. Now does very little activity, in part I feel the degenerating of brain neurons from the Parkinson's made her worse. She also forgets new things now like new people she meets, if she greeted you, if she ate, if she went to the bathroom or even that she just showered for the fifth time that day. I have recently begun to care for her for a few hours three times a week while my mom goes to work and my dad gets home. I had to really think about it because she has moments of frustration and reacts in mere fits. I also had to think do I feel like dealing with repetition and her talking non stop about a life she wishes she could live. Then I had to pray about it because it is not so much thinking as much as feeling with my heart what I felt when I was 9. To care for her is challenging at times because unlike us "normal" folk she wears her feelings on her sleeve is honest and stubborn at times. In those honest and stubborn times I see how "normal" is actually is and how we can love someone unconditionally.
I have learned many great things from her and continue to face the same truth...we really love children unconditionally as Christ does because we have to have faith in them, trust them, forgive them, give to them, and most importantly love them!!! Now that I am a mother I understand more how and why my mother loves us so much even in our imperfect lives and disabilities  because we are a great gift from God and she feels honored to care for us no matter what circumstances life gives us!!!!! So thanks be to God for my mom and for my sister, to teach me life's most important lessons about unconditional love!!!!!! :)