Actually we all have a responsibility not to cause harm to a stranger and her children. The OW is therefore not without blame. I think I know your original thread and therefore as in most cases, the OW certainly did know your H was married with children.
As a general rule, I only ever recommend contacting the OW if it's to verify or find out information and if contact is made it should always be personal and not by text or E mail, but Belle's suggestion about writing a letter that you might never send is a good one, because just writing it all down will be cathartic.
It's also never a good idea to make contact when you are feeling angry, mainly because your perfectly righteous anger might harm you more than her. If or when you ever have contact with this woman, it will give you more satisfaction if you are calm and logical. You also need to anticipate all her possible reactions and the effect they will have on you. You might be too fragile atm for example, to cope with sneering contempt back, or lies from someone with a massive axe to grind, now that the relationship has presumably ended.
You might find it more helpful if you either update your old thread, start a new one about the recovery process, or talk more on this one, because I've seen your posts over the past week or so and I know that you're struggling, a situation with which I have huge empathy.
It is not iniquitous at all to feel angry with the OW, but of course the person most deserving of your anger is your H. Your story demonstrates why drip-feeding the horrible truth is far worse than coming clean straight away. If you are going to survive this, it is essential that you make some new conditions about hearing the whole unvarnished truth now, because every time there is a new horrible revelation, it will take you right back to discovery day and the healing will be frustrated.