My little sister has epilipsy. nearly 10 years later, my little sister tells me that our older sister broke a plate on her head when she was little. it was around the time my little sister developed epilipsy. could that event have caused her epilipsy?

In medicine we are taught to never say never, yet in 4 decades of seeing kids who develop epilepsy, this is not one of the links. If the cited plate braking did not put her into the hospital, I cannot see it as a cause. In many cases there is never a clear cause even after years of investigations looking for one.

If the prior head injury did not result in neurological symptoms at the time of the trauma, it would be very unlikely that she developed post-traumatic epilepsy. Most likely classification remains in the realm of "idiopathic".