I'm very sorry but not surprised that Cousin reacted in the way she did. I imagine she is not only scared and angry, but also ashamed. She shouldn't be ashamed, of course, but I suspect she is. It doesn't excuse her lashing out against Friend of course, but it does explain it.
I hope very much that she will remember that Friend is there if she ever needs help, but in the meantime, I would honestly advise Friend not to keep texting her. Friend has done all that she can, and it's now up to Cousin.
Regarding the husband, I'm not sure what to make of his belligerent behaviour. It could very well be down to guilt, or perhaps he's just naturally an overbearing kind of person.
OP, please do reassure your friend that she has done the right thing, but do urge her now to step back, unless Cousin contacts her, or unless she has absolutely clear evidence that Cousin is in danger.
I really hope all will be resolved well, however that resolution occurs.