You can't do anything about it, other than--in the course of proceedings--providing your evidence or documentation to the contrary (which can generally hurt youd daughter-in-law's case, by damaging her credibility, which will help your son). The reason you can't do anything:1) First and foremost, there is a "litigation privilege" for comments made during court proceedings--they are not considered actionable slander or defamation. People are allowed to make incorrect statements during legal proceedings.2) "Ill health" is a subjective term, as is her assessment of your ability to care for the grandchildren; it is not unlikely that a court would simply consider this her opinion, and everyone is legally entitled to an opinion.