Summer vacation is typically a time when a teenager can go days in the same house as his/her parents and won't be seen the entire time.
I wouldn't chalk this up to truely horrid parenting, just mildly, and understandably neglectful. It's just not generally worth the attitude to intrude on a teens fortrace of solitude when they are in a hermit mood.
She probably figured he was emerging late at night and she just wasn't seeing all his foraging and shower breaks.