How is it her first kill? <spoilers>

If this is a prequel, I assume the title references the destruction of the family that all die (Julia Styles et al.)

However, this isn’t her first kill, nor are any of the others - pervy security guard at the institute, art teacher from the institute, the detective etc.

Also, the film references what became of a family that had her before (can’t recall if it was her real family or the first family who adopted her) who all died, assuming that she killed them (which she must have?!)

So this title seems weird and redundant?!