spouse or parents

i know of a couple in there early 20s that wants to get married. problem is the female  is of a particular religion. and her parents have done everything they can to stop this wedding. only on grounds of religion. this female doesn't want to alienate her parents but also wants to marry this guy. my question is should parents even have a say at this point in life. if so at what point do you quit interfering in your kids life and trust them to make good decisions.i should add the guy is willing to convert just to appease her parents. i think this is wrong too. but really not my place to say so since I'm not religious.