When I was in the school system, we had PPW, a pupil personnel worker. They were involved in all situations outside of the school, that impacted attendance at the school. In our school system, boundary issues were big because families would fabricate documents that indicated a child resided within one school district or another and they would try to establish the actual address. But absenteeism to the extent you indicated was definitely another area they were involved in.
I haven't read all the responses, but I definitely agree that an immediate team meeting including the mother (if she attends) is in order and could be justified by the impact these absences are having on the child's learning. While at the meeting discuss the school's need to be prepared to meet the child's health care requirements while in school and get a release of info signed for the pediatrician. If the child does not have a primary care doctor, work to meet that need etc. Also.. if the child has a met a certain number of absences, is there a home/school requirement that kicks in? If so, the mother may be freaked by having someone come into her home and may be more helpful. Re CPS, we were always told that as mandated reporters, we don't screen our calls. We call if we have a concern re neglect, abuse, whatever and the agency does the screening. ie, there is no bad call. I also always like to think of the CPS call as finding another avenue to help get the family the resources they need to deal with the situation that's causing the family distress. The county/state/school has resources available that as a school nurse you may not be aware of or know how to plug the family into. I've also made conversational calls to CPS, just to get their thoughts. Perhaps there's some sort of a county program that could be recommended to this mother since her child "has" so many chronic illnesses (etc) ostensibly to help her deal with the health care system but maybe to assess what's going on and help organize the family into a healthier level of functioning. . I also worked in inpatient pediatric psych so we did a lot of followup and trying to engage community systems. And you know.. although I haven't been part of the school system for a few years, when I was, it was with a very needy community with significant barriers of every kind including language. I sometimes found the offices of health care folks I reached out to were willing be a little flexible with the intent of helping the child and family. Good Luck!