Do not give her more dosage of lithium without a Dr. Lithium is very powerful and too much is very toxic very bad. Too much could do very much damage. Only give her the amount the Dr says to give her.
Tell the Dr. you find it difficult to give her the Lithium in the morning. Ask him what times of the day to give it to her because it should be spread out in my experience. Make sure if your going to keep her on Lithium that you give her the dosage the Dr. prescribed in order for it to work. It is also important to get her blood levels checked periodically since she is on Lithium. They want to make sure she doesn't become toxic. I am taking Lithium capsules which work better for me and I think it is a good medication. Tell the Dr. all of her symptoms so he will be able to give her the right medicines. Sometimes it takes a while to find the right meds that work together to help. Hope this helps some. You are good to take care of your sister like this. If you have any more questions we are here for you.
My way to know if I am okay is to ask myself 3 questions.
Is she in danger?
Is she hurting anyone?
Is she getting worse?
If all the answers are no, then she is okay for now. Bipolar moods change, she just needs some time. Laughing and talking to herself doesn't hurt anyone, so I say let her do what she needs to.
Remember. We are not Drs. But volunteers.
Your sister is 21 yrs old. Can she ask her question? What questions do you have? We are here to help. Maxy