She doesn't sound like a crazy person at all. She sounds like someone who is in shock having received a request for a DNA test for a child that her husband may have conceived before their marriage.
That means that the child must be at least 18 months to 2 years old. That is a huge thing to accept.
Most women in this situation do tend to start off in denial/very angry etc. And that is entirely understandable.
Her whole life is now upside down, instead of having a life that includes her husband, his first child and all the accompanying arrangements, familial realationships etc she will now have to create a life that includes integrating a second child into the family along with all of those associated familial relationships, arrangementts etc.
In this situation contact is often very difficult as the child will not have had any interaction at all with it's father. There could be a protracted legal process to go through if the mother is opposed to contact which will undoubtedly cause a huge amount of stress for all involved.
If the mother is not opposed to contact then it will have to start off as supervised, then slowly moving onto unsupervised.
In many cases the mother is opposed to the wife/partner being present at contact and will cite the reason as "the father needs to et to know his child" which can cause resentment between the wife and her husband as she will feel sidelined.
I could go on here but tbh I don't have the time.
Throwing insults at someone who is shocked confused and upset is not the way to bring about a decent conclusion for all concerned.
Talking it through and helping to counteract any objections however is much more effective.
For what it's worth, my dd's father has nothing to do with her and his wife has said that if he ever changed his mond she would leave him. I haven't taken offence at the op's posts.