My ds was the same at as similar age and still is now sometimes at 12. I taught him lots of the techniques I learnt having a squillion years of therapy for anxiety and OCD/intrusive thoughts, they are based in mindfulness and ACT therapy.
I have always taught him that it is important to recognise and acknowledge the thought as it comes in, while remembering that it is just a thought and thoughts arn't real and cannot hurt you in any way, but trying to 'get rid' of bad thoughts is usually extremely counter productive as is distraction. Instead we 'thank our mind' for the thought and welcome it which I know sounds bizarre and totally woo, but bear with, it is very effective. You also give the thought a label and name as a 'story' if possible (as most thoughts are repetitious), so it would go something like this -
Have a bad thought ie imagining you dying (sorry just an example)
She say the words (aloud or in her head)
'Thanks mind!' or 'Thank you mind'
and
'There's the story about my mum dying again, thanks for telling me that one'
And the thank you need to be genuine, not sarcastic or sad (I struggled with the sarcasm bit for ages 
bastard mind), genuinely thank your amazing, imaginative, incredible mind.
I KNOW it sounds barmy, it took a lot of persuading me to do it, but it really works, interestingly ds just took it at face value and it worked straight away.
For very persistent thoughts or another strategy if the above does not work, is to sing bad thoughts to a happy tune, I like 'happy birthday' and also 'she be coming round the mountain' but any perky tune will do, so (hapy birthday) -
My mums going to die
My mums going to die
My mums going to d-ie
My mums going to die
The more you sing a thought the more ridiculous they sound and the more your brain will 'unfuse' with the scary feelings, this method is really effective.
But the key is, it is all about defusing and dispersing thoughts, never about distraction or avoidance.
Also useful (if you haven't) is to tell her it's really normal to have such thoughts and not to think it makes her unusual or 'bad' in any way.
Also remind her that we tend to listen very hard to the negative voices in our head and attach great importance to the things they say, so if she thinks 'I am not normal' or 'I will have a terrible day at school today' she is likely to believe that thought, suggest instead that she thinks 'I am a unicorn' or 'there is a million pounds under my bed' - does she think those could be real now she has had the thought? All the above are just thoughts, but our minds are generally wired to attach credence to the crap ones, some more than others.