I had a similar circumstance. I was a school nurse for early childhood special education. A preschool run by the school district's community department, but not under my authority, had told me I was not an employee of theirs and I was not to touch their clients. My job description was clearly for the special education preschool students, some of whom were mainstreamed in the preschool classes, but it did not specifically exclude the regular preschool students. We assumed it was a fee issue. They charged the pecial ed services mega fees for placing the special ed kids in their preschool classes because they ususally took up so much space and had so many adults providing services, they could not enroll as many regualr students. One kid on a ventilator took up the space of three paying children with his equipment and 1:1 nurse and special ed teacher. Due to several medically fragile kids, I was in and out of the classrooms on a regular basis and many of the parents knew me on sight. I think they assumed I was a school nurse for the building. There was also an outside agency that ran a before and after school program in the building that my job description clearly excluded.
For the preschool kids it was quite a dilemma. One time I was asked to check for lice without touching a child - ??? When there were contagious outbreaks, hand Foot and Mouth, Fifths Disease, Lice, that affected my students and theirs - I did send the note home with the whole class after the preschool approved them.
One time a preschool child had a freak fall during activity time and dislocated her elbow - I did not know that at the time, but I was called and it was clear to me that the child was in shock from the pain. From the deformity and the pain, I thought it was broken. None of the managers for the preschool were in the building or able to be located - they were at district meetings off campus. No one working for the preschool seemed to know what to do.
I took over, applied ice, elevated it, located the parents, and stayed with the child until the father arrived. I did page my supervisor to let her know what was going on.
I did not get in trouble from the preschool managers for stepping in, but they were not overly effusive in thanking me.
I think it is important to get a clear direction from your supervisor regarding the district policy. It would be important that the contracts with outside agencies cover first aid and emergencies and whether the school nurse is a part of the package. On the other hand, in an emergency, you would be liable for not assessing and taking action, even if it was a vistor to the building.
For other legal problems, an excellent book that won a AJN Book of the Year award for 2001:
Schwab, N. C. & Gelfman, M. H. B. (2001). Legal Issues in school health services: a resource for school administrators, school attorneys, and school nurses. North Branch, MN: Sunrise River Press.
It can be ordered from amazon