1. you will not get the fathers approval unless you are of the same faction, if you are otherwise an owner of your own fief/court. She an be convinced to elope with you. I once married within kherjiit and broke away to my own kingdom. I did not put the leg work in to convince them to join me, but needless to say, it did not give me any benefits towards the Kherjiit.
2. If she is betrothed to someone or is seeing someone, the awareness has to be engaged by her, that she is whoa oh so in trouble for her heart to you but her bond to them. can be split by forcing a duel on the said lord.
if it is the father of her saying she is seeing another guy. i am pretty sure you got to do some serious woop ass to over turn his opinion which might not happen in time. so if you arent of the same realm and you want her. spoil her right as she likes. and get her to elope with you.