Mums strange lie

That's really strange and I can see why you're curious about the tattoos now. If your mum was upset back then and scrubbing her skin then that indicates that it was something that she didn't want. Possibly something against her will.
I'd ask her about the tattoos now.

this happened when you were a child - it was something your mother did not wish to share with you then, nor now
why are you unable to respect her privacy?

You said you don't need to know what happened, just that something did. This is making it about you rather than about your mum's trauma. Please don't do that. For whatever reason your mum doesn't want to talk to you about this. Please respect her decision. You have no idea of the pain you may cause her by making her think about this, much less trying to make her talk to you.

I would say cult/ witchcraft.

She probably got out of it if you were not aware of it growing up, which could be why she doesn't want to talk about it.

I think you need to make your peace with the fact that you'll never know.

@Janiie when has the mum said these images are upsetting?

Just some questions, OP

1. Could your mum possibly have drawn the marks on her own body, or were there straight lines on her back?
2. Were there any marks on her face, neck or hands?
3. What colour/s were the marks?
4. How do you know that the current marks are tattoos and not drawings?
5. You said that she'd changed, after the incident. In what ways had she changed?
6. Was there anyone else in the house at the time?
7. Have you mentioned this to any other family members?

My first thought is that she was involved in some kind of cult/witchcraft? Does this seem like something your mum would get involved in?

Maybe having the arrows/dots tattooed shows she still has some kind of connection to it.

It is so difficult as she has denied it happening but something did happen.

I wonder if you can say- I don’t need to know anything more than my memory is real and not imagined and anything else is totally private. I will respect that. And if you do want to talk to me then I am here to only listen.

You’re not going to get a resolution or answer,clearly she’ll not discuss it with you
All you can do is mentally file it under unknown and I would not persist with seeking an answer

Not all would. I assume they only would if they wanted to...if the mother here doesn't want to there is absolutely nothing wrong with that!

Yes and they would share their experiences if asked.
Look, the parent doesn't have to tell her anything it is just a very weird thing to do. Say it didn't happen then get a tattoo of the very thing that didn't happen.

Many concentration camp survivors viewed their number tattoos after the war as a sign of resilience over what they'd endured. The OPs mum may have got hers done for similar reasons. Still doesn't mean she wants to talk about it though.

I disagree, that if you saw something as a child, you have a right to understand what it was, especially if troubling you.

Everyone is entitled to privacy, but you saw this and thus she should kindly explain, or at least give some explanation.

ie. I was spending time with some people and they did this, it upset me, I’m sorry it disturbed you.

It doesn’t have to be all the details.

She's told you repeatedly, leave it alone.

She has got a tattoo of said upsetting images. It is bound to bring it all back and raise questions.

I wouldn't ask again.
You have asked multiple times and your mum has not told you anything despite having been given the opportunity. She obviously does not want to tell you, surely you must accept this.
Why do you think your right for information tops your mums right to privacy?

Just say 'Something upsetting did happen I remember it clearly, please do not gaslight and tell me it's all in my head You now have tattoos which obviously bring the whole thing back. What happend and why all the secrecy yet a tattoo which will raise questions?'.
Good luck.

The new tattoos might be a sign that she's processing things and perhaps more ready to talk.I would chose my moment but I would completely wade into it, ask why these tattoos look so much like the signs she was scrubbing away that day when I was 7. And I would tell her that I've been upset by that memory ever since.

She can't erase you out of the picture, you were there: she doesn't have to disclose what she doesn't want to disclose but she owes you an explanation.

Kindly....question yourself....why do you need this information?

My parents are dead, there are many questions. It's hard.

What her mum chooses to do with her own body is her business and nothing to do with anyone else.

The OP has the right to ask for clarity, the mum has the right to refuse. If that causes the OP turmoil then she must find other ways to deal with it. She cannot keep chipping away at another person, who has the right to privacy.

This. If you genuinely do have this memory, and it isn't an inadvertent fiction, then I would say you should leave this alone...you don't have the right to know everything.

And her mum has every right to privacy, especially if she has lived through something traumatic. People don’t get tattoos for other people, they do it for themselves.

She's had tattoos of the images! If she wanted it to be left in the past why on earth bring it all back up again.
The op was a dc disturbed by what she witnessed she has every right to ask for clarity.