She couldn't have spent two years at the high school before 1958--the school didn't open until 1957 and it admitted only the class of 1959 as Juniors. I believe the class of 1960 was not admitted or if they were, it was only some of the students.
I suppose you might think that the class of 60 was also admitted in 57 as sophomores which supports your two years to the end of her Junior year. That's possible.
Forget what I might think, go by the video. I’m an Australian, I keep telling you, I have no idea what a frikken sophomore is.
To the best of my knowledge that high school commenced taking students in 1956.
And I’m certainly not responsible for that video content.