The National Enquirer quoted as saying....
"After abducting Elizabeth, the fiendishly clever Mitchell helped win her trust by exploiting a rebellious streak in her -- making her feel like a young adult free from parental bonds.
'Elizabeth, like most girls her age, had begun to clash with her mother,' said the source close to the investigation.
'She had a crush on a boy in her class. But her parents, Lois and Ed, told her she was forbidden to date until she was 16.'
She also begun to favor punk music. She talked about getting piercings and dying her hair black. She was fascinated with the whole gothic lifestyle.
Mitchell's mind control manipulation tapped into that part of her personality."
If the above is true, then Lois and Ed knew she was interested in boys despite their denial. , but I think it is pretty normal for a 14 year old to be interested in boys despite Ed and Lois' adamant denial that Elizabeth was not interested in boys.