That certainly seems possible. Having only attained the lofty rank of SP5 (E-5) in the Army I know very little about the service academies. But if she was a "freshman" she would have only started days ago. I know that the academies start rigorous PT very early so it seems possible that she,as a result of that PT,had some kind of undetected heart condition that killed her.
Like I said...the family should get an independent autopsy.
re.
"...she would have only started days ago" Her class started basic training on June 26 and wrapped it up late August, so she's already been there a while. At least she made it through basic. My first roommate tried to commit suicide after our first full day back in June 1969.