Lets take the last part of your question first. Conventionally, bipolar disorder is treated with a combination of mood stabilisers - such as lithium - and anti-depressants.
Antidepressants must not be used on their own, since they can trigger manic episodes in bipolar sufferers.
As to what specific drugs in each class are used, it is often a matter of trial and error to find out which are tolerated best by the patient, and which have the best effect. We all, as individuals, react differently to any given medication.
In addition the type of bipolar disorder may also be a factor in choosing a medication. In addition, anti-psychotics may be of value, but what to choose as a suitable combination of medications is best left to the physician who is best acquainted with the individual.
Amnesia, or lack of memory of behaviour during bipolar episodes is pretty well normal.
Sufferers may have short term memory loss, or even memory loss which covers several weeks, being unable to remember what they have said or done during that time.
As to the risk of violence, about 10 to 15% of people with bipolar disorder have a violent episode, and these are often triggered by alcohol or drug use, or extreme personal stress. Mostly, they harm themselves rather than others. While you cannot totally discount threats of violence, the probability is that they will never be followed through. It is simply a matter of being vigilant, and if you fear at all that there is a possibility of violence, contact the police.
Finally, if she is not compliant with her medication, she is a much greater risk, and all the family's efforts should be directed towards making sure that she is compliant. It's also important that all of the family educate themselves as much as possible about the disorder, just as you have done. Please make sure that her parents look at the information here. It is extremely valuable.