Christine Lonas was a tool of Dar Adal in season 6 and abused the power of her office to harm Carrie–and Franny.
I was surprised to see her back because I didn’t expect the show to make that effort. But it added to the realistic buildup of the courtroom scenes, because of course Franny’s case worker from a former (well, less than 6 months ago) custody battle would be questioned during a new hearing.
Given the number of wrongs Christine Lonas leveled at Carrie in season 6, and given she betrayed the integrity of her own office, and given the fact that Dar Adal is out of the picture this time and it’s a real custody case and not one with some predetermined outcome… I was glad to see her undergo a change of heart. Not necessarily because of what she said, but because this is what you’d expect from a person in such a powerful position, able to alter the lives of the parents and children she interacts with.
Furthermore, at the end of season 6, Lonas played supposedly an active role in Carrie getting Franny back. Questioning her own judgement now in a courtroom less than six months later probably wouldn’t make her shine.
But overall, my interpretation is that she knows that she caused a lot of harm and grief in New York and that she owes Carrie and Franny an honest and true statement.