My poor sister...

So we went on a trip recently, my sister is 8 years younger than me. So obviously I’m the person she comes to about sex questions. (She’s over 18) so she tells me that she’s had sex but can’t have an orgasm with a guy. But that she can cum...and I didn’t know how to explain that they are the same thing... aren’t they? I’ve read a couple post on here saying the same thing and I have to say it. If you don’t orgasm...you don’t cum!!!! How are they not one in the same? Is it bc they’ve never had one with a guy that they don’t know? Idk...just bothers me