As Og is my witness, I’ve read about this very subject on Slate or someplace within the past few years. Basically a teenage girl was dying of some terminal illness, and she did not want to die a virgin. She had a friend-with-temporary-benefits (or maybe a boyfriend) who was willing to step up, so to speak, and her parents were OK with it too, but the hospital was having none of it, IIRC.
You’re probably thinking of this 2001 Australian case, where a terminally ill 15-year-old boy’s Make-a-Wish was to lose his virginity.
I keep looking at the title of this thread and wondering what terminator 3 had to do with teen sex.
I agree with everything WhyNot said, except that I probably would help my terminally ill teen if it didn’t embarrass them too. Hell, they are about to die. If they need mom’s help in some way, so be it.
I think if I were the dying 13-19 year old and I wanted to have sex–and my parents didn’t want me to have sex–I’d say to hell with them. There really isn’t any incentive for the dying person to give two fucks(pardon the expression:p) what their parents think about the whole situation.
So with that in mind, I wouldn’t encourage it–but I wouldn’t try to prevent them from having sex either.
Unless it involves the suffering of others, a dying primate is entitled to decide for themselves how they’ll spend their remaining time on earth.
There is if they’re worried they might go to hell if they have sex, and they’ll care more about that than most teens since they’re actually dying soon. Then their parents could either confirm that yes, they will go to hell if they have sex, or reassure them that they won’t.
I wouldn’t worry about that if I were you 
A beloved young relative of mine did die young. I’ve always hoped she did.
Would the gender make any difference? No, all long as she had a nice time, boyfriend or girlfriend wouldn’t have mattered.
Yeah, me neither. I wish I’d been bulldozed by a few powerful teenaged girls with big personalities back when I was 15 or 16. Or 17. Or 18.