Even if they were married his only obligation would be child maintenance, courts don't always award spousal maintenance, and it don't think they should either.
Women are in charge of themselves, and if they want to become SAHMs, married or not, then they need to a cote that they have next to no financial security.
Wanting him to have to pay for a divorce lawyer or pointless mediation is just spiteful, albeit possibly understandably in the circumstances, especially considering that she would have to pay for a divorce lawyer too.
Marriage is incredibly important to me, that's why I'm married, but I had children with my ex and we weren't married. If we had been, it would have just caused extra stress and hurt that neither of us needed. He's still a very committed parent to our children and is a supportive co parent to me, marriage would have made no difference.
The problem here isn't the lack of marriage, it's the lack of financial security your friend has. And that is completely a result of her own choices, she has no one else to blame.