The schools have graduation requirements, and they are well known to every entering freshman.
That said, I find this amusing because I was also short gym credits and was told I wouldn't graduate. Their solution? Put me in three consecutive hours of volleyball until I had enough credit.
Of course, that was 1976. Different times.
But she didn't enter the school as a freshman. Her previous school counted the varsity sports (most count any level of interscholastic sports) as a PE class.
She shouldn't have dropped the PE class, though, assuming she only needed the one, but OTOH, she doesn't really need that degree and so can just say "screw it", which is just what she did.
This is yet another one of those sob stories we get at this time of year involving high school students who can't seem to follow the rules and expect them to be bent or overlooked in their particular cases. And of course, in the unending struggle against the left-wing public school system, no conservative principle (such as discipline and respect for legitimate authority) is so sacrosanct as to not be sacrificed.
Seems to me the student could have gone to a community college to get the extra credit. The mother made the decision, now has to rationalize her rebelliousness.