Regardless of the reason he was fired
she needs to be able to support the kids by herself. As others said; what if they were still married and he lost his job? They would have to make it work on one income there. You said she has a great apartment that she will be able to just barely afford. That means it is too expensive to her. Will there be any proceeds from the sale of the house? If so; can she go to court for a bigger split of the proceeds or all? I had a family friend that did that and instead of always having to fight for child support she just took all of the proceeds from the sale of their home and let him walk financially. I grew up in a divorced situation and my mom never saw child support. He always worked under the table so he could afford to live and didn't have to pay. My dad passed away about 10 years ago and she just received a letter that due to his passing she would not receive any back child support. Duh...really????
My mom being able to do that though gave me great work ethic and should anything happen between my DH and myself (lets face it we never think it will but it can), I am able to care for the children financially myself.
Child support is tricky....what if she took a job with less money and brought him to court to pay more because of it - should he have to? This is the reverse...he will be getting less money thru unemployment. Is it right; no.
Hopefully, there will be proceeds from the house. In the meantime see if she can find an apartment that she can comfortably afford and not just barely. Good luck to everyone involved.