Haiz, it's kinda late already.

The correct procedure:
1) Your sis should have been sent to psychology center for therapy to identify the exact cause, or to confirm it is only learning difficulty or resulted from other mental issue.
2) Never ever use medication before even giving her consultation or therapy - medicines have side effects, and it can't treat the root cause.
3) Your family should have treated her nicely to give her positive energy and motivation. She would have then be more understanding and independent.


Now, if your family still treat her as a real family member, I suggest the following:
1) Change your attitude, be nice and empower her.
2) Bring her to psychology centre for consultation to find out the root cause. You will be surprised many mental issue can be lighten or treated without medication.
3) Dpn't just feed her medication blindly. Medication is only temporary solution and never tackle the root cause.

Suggest bring her to psychology centre for assessment. Just wondering which area do you live? If puchong area I can suggest Turning Point, affordable and good quality (Owner is Prof in psychology, and most staffs are buddhist). Rate around 100 something per hour, but if your finance is not good, can nego.

Try your best to recall your sis's symptoms during her childhood / teenage time. These will be very useful during assessment.
Didn't your doctor recommended your sis to engage psychology professional before prescribing medication?
Your family / relative got history of mental illness or not?

Good, lower case of having inherited mental illness, hope your sis get well soon!