My mentally retarded sister suffers from epilepsy even after many medication. Why?

Hello doctor,

My 13-year-old sister has been diagnosed with various mental disorders since the age of 2. My parents have taken her to doctors since then because they have noticed that she was not developing like the other children. Almost every doctor gave another diagnostic such as autism (each doctor suggested a different type of autism) and mental retardation. When she was approximately 6 years old, she was also diagnosed with epilepsy. At first, the crisis was happening only while sleeping and they were detected during an electroencephalogram (EEG) by a doctor. He prescribed the first anti-epileptic drug which was Ospolot. My sister felt very sick from it so another doctor told us to stop the medication. We did and then she started having a different type of crisis, absence crisis while awake. The doctor then prescribed Topram. Throughout the treatment with Topram, another type of crisis was added beside the absence, that is myoclonus. The doctor then prescribed Depakine instead of Topram. The absence crisis stopped, but the myoclonus stayed. Besides Depakine, she started taking Rivotril as well. With this combination, she stopped having a crisis for 3 months, but then the myoclonus started again and nocturnal epilepsy crisis was added as well. During this period, the doctor tried to replace Depakine with Lamictal (Lamotrigine), but my sister became intoxicated from it and started suffering from the Stevens-Johnson syndrome. She had to be at the hospital for one week to detox. My parents went to a different doctor then and he added Topram (Topamax / Topiramate) besides Rivotril and Depakine. This did not work again. My sister felt very sick from this combination while having a crisis both while being awake and asleep. She was then prescribed Depakine and Levetiracetam. The crisis while being awake stopped, but those while asleep still happen. At the moment, she takes Depakine, Levetiracetam, and Ospolot, but the nocturnal crisis persists. We do not know what to do anymore because the side effects of all these anti-epileptics have done a lot of damage. My sister is always very sleepy and drooling all the time. She already has mental issues so this just makes things so much worse. I know I wrote a lot, but I thought you should have as much information as you can. Here in our place, doctors are not that well informed about these diseases, so they do not really know how to deal with it. We also cannot afford to go to other countries anymore to check with other doctors. Any advice is very welcomed.