I think OP knows what she did was wrong.
She has taken advice on board and decided to wait before reacting or making a decision.
Whatever her motivations for doing so - hurt/revenge/actual cruelty/misguided sisterhood - the question remains...
Should she tell OW?
Several people on here have said they would want to know. So would I. I?d want times, dates and proof. I suspect my EXDH did have an affair but I couldn?t find any proof (wasn?t on MN then eh?) and I wish someone had told me.
And actually, I?d keep both texts and videos if you do plan to let her know. Here?s why...
Similar happened to a friend:
My friend decided to let OW know. Her motivation was that he had just proposed to his girlfriend and she felt the women should know just what she was marrying.
I disagreed, for the record, as I figured she would find out for herself and wouldn?t thank her.
Anyway, she arranged to meet her face to face and calmly told her how long, when, where and apologised. She offered to show texts as proof and gave her number if she wanted it.
OW refused to believe her and stormed off.
GF then confronted the twunt who assured her my friend was a stalker psycho, had brilliant excuses and denials for it all. I was there when he then rung my friend, went mad, told her he would always deny it but that he?d still like to see her!!!!
I was also there when OW confronted my friend, drunk, surrounded by her ?gang? in a pub a few weeks later. OW?s friends were demanding proof, calling her every name under the sun, asking me and others if it was true. We all said it was, we?d seen them together, but it was over now. My friend showed her the texts.
She went on to tar my friend as a slut all over town and last time we saw him, he was laughing at my friend across the bar telling all his mates how he?d got away with it. She was left humiliated, hurt and angry.
They got married, but he texted her while on honeymoon pics of himself naked and he is sleeping with at least three women while his wife is now pregnant.
I?d be careful about telling her, regardless of intention. But I would keep texts in case she ever confronts you. And if they don?t believe the texts, maybe you do need the video. But I?d never offer it or let its existence be known