NES and Epilepsy correlation?

My friend (age 31) was diagnosed as having epileptic seizures and NES occurrences (via 2 different EEG tests).   Has there been any correlation or study on the interralation of the two types?  Can NES be a contributing factor into developing full-blown epilepsy or vice-versa (i.e. trigger)?  The seizures started at age 25 and there has been some severe psychological trauma experienced throughout her life including sexual abuse during her late teens and loss of her mother at an early age.  All of the research I've reviewed so far treats the two seizure-types separately.  Any research/studies that you could point me to would be appreciated.  Thank you.