Risperidone is an neuroleptic (anti-psychotic) drug basically used for treating schizophrenia and mania. It is also used for treating psychotic symptoms (hallucinations) and aggressiveness in some neurological disorders like dementia.
In cases of dementia anti-psychotic drugs should be used in doses as small as possible in order to minimize the side effects. Sleepiness is one of the side effects. In case of Risperidone that would be 0.25-0.5 mg twice a day. You can try to decrease the dose to 0.25 mg twice a day.
Her aggressiveness can be also due to anxiety. In that case antidepressants (paroxetine, sertraline) may have better effect.
You should consult some neurologist about all these possibilities.