Record her telling you to give her oral then say no. She's obviously bisexual/lesbian as well so you have something over her, too. Get your sister help. She obviously needs it as desire for incest is abnormal.

I agree with Dusk - your sister is very likely a lesbian too so anything she thinks she has on you, you also have on her. If she is not a lesbian then she may have been sexually abused by a female because she exhibits classic signs of being sexually abused and then turning to abuse herself - manipulation and blackmail.

She does need help and the sooner she gets it the better chances she will heal. Plus, if she exhibits this behavior with you, who else is she doing this with?

After all you have been through I would urge you to also find a therapist because this is the type of experience that has a way of sticking with you if you don't heal from it.

Take care

I hate to say this but I agree with the others that, in this case, fighting fire with fire may be a solution.

She may be bluffing. It would be a gamble, but you could just tell her to buzz off and cross your fingers that she won't do anything. It depends on how desperate your situation would be if your parents disowned you.

thanx for all ur advice, im taking it all onboard and deciding on a descision, thanx to u all