There are a few things that I see going on here. And that’s really good news, because it gives you a bunch of different avenues to approach this.
I get that you think this is a destructive and even almost evil thought, but when you really think about it, it’s not really neither destructive nor evil. I mean, if she really did have cancer, then we’d be calling this a factual thought, right?
And if she didn’t have cancer, then what are all the labels that we could apply that’s not “destructive” nor “evil”? (Take a moment to think about that now, before reading on. I’ll wait…
…Did you think about it? Excellent! Good for you.) Whilst you were thinking about it, I was thinking about it, too. Two of the labels that came to my mind were
- “false,” as in “I had this false thought, which was not true” and
- ““unreal,” as I had this unreal thought, which was not based in any tangible reality.”
So, one avenue that you can use to approach this situation is to be more discerning about the labels you’re using to describe your experience. Me, personally, I would choose labels which are true and which empower me and amplify what I’m doing right. (From what I see those labels from your post didn’t fulfill any of these criteria.) In the beginning, this choosing will take some awareness and decision on your part, but no more so than the awareness and decision that you used to learn any of the skills you now possess.
Let me make sure I’m understanding you correctly. Are you saying that you think that, because you think this thought, you’re going to give her cancer?
Because, as much as I believe that you are powerful creator (it’s there in your screen name, after all 
), you’re not that powerful. Unless you’re planning a spill of toxic waste or bombarding her with radiation, you can’t give her cancer.
Now, I get that you wouldn’t want to think it. It must feel uncomfortable for you when you think it, even before you judge yourself after thinking it.
But here’s the thing. It sounds like you’ve practiced yourself into a bit of habit. To me, habits are like playground slides. I don’t know if they had them when you were growing up; heck, I don’t even know if they still have them in my country now. But if you’re familiar with the playground slide, you might remember that as you climb the ladder to approach the slide part, even as you sat on the platform right before the slide part, all those places you still have some control.
But if you go just a smidge past the places where you still have some control, you’re off, sliding down the slide. Wheeeeee! IOW, at that point, when you’re sliding down the slide, there’s not much you can do about it. You just have to let gravity have its way with you until it brings you back to a place where you once again have your control.
And this is sort of what you’re describing. You start your story once you’re sliding down that slide and gravity has its hold on you, and where you don’t have much control.
Now, it’s all right that you’re starting your story there. That is part of the story, after all. But that’s the part of the story where you don’t have very much control (and, of course, you don’t need me to tell you that; I’m sure you’re well aware of that already).
But here’s the thing. Your story doesn’t start where you are starting it. Like my story about the slide, where we see the slide, where we decide to play on the slide, where we walk over to the slide, where we climb up the slide, where we seat our rumps on the slide and prepare ourselves to push off and let gravity give us that Wheeeeeeee! experience, there’s more to the beginning of your story about your thoughts. Now, you might not have been noticing that more-to-the-beginning of your story, but it’s there and you can start to notice it.
And as you notice more and more of the beginning of your story, you will also notice that there are places in your story where you have more control and where you have less control. And noticing those differences is key. Because if you try to make changes where you have no control (like in the story as you told it to us), your options are way, way limited.
But when you start to notice those parts of your beginning that you had been overlooking where you do have control, then you can start to come up with things you can play with so you don’t go Wheeeeee-ing down that slide until you want to.
If you’re like me, you learned how to do it with a slide. You can learn how to do that with this, too.
You lost me. “…ruin what?” Because you’re not giving her cancer, so you’re not ruining her in that way. So, what are you meaning?
Remember our chat (above) about “labels.” Look at the labels here and how you’re using your labels. Let me help you out some by highlighting the labels that I’m seeing:
“…make everything … twisted and perverted…”
So, think about these:
- What’s everything in your experience that’s not this experience?
- What’s everything that’s in the universe that you hadn’t included in your first answer that’s also not this experience?
If you really considered those questions, you’ll see that there’s a whole lot of EVERYTHING that you’re really not twisting or perverting. And I don’t say this to make you wrong. I do say this to invite you to open your mind to new and different ways you’ve been looking at your world, including this experience, to see what else you hadn’t yet been noticing.
(Now, you’re just kicking yourself when you’re down. What benefit do you derive from that?)
I’ve found (and I wonder if your experience will be the same) that online forums are not the best place to do therapy, which is sort of what you’re asking us to do with you here.
Now, the good news is Cap’n has made, for us, a therapy field: My personal emotional and mental supporter, which you could use to discover the answers to these questions for you.
When you have your answers, I’m sure they’ll inspire you to certain other fields to help you work through your issues.
Now, the one thing that you’ve told me is that you are willing to beat yourself up. So, that leads me to suggest JAAJ’s Daily Self Love Stack 
and Self Love Transcendance to you.