Pretty sure that Ford was one promiscuous teenager...and a gd liar....otherwise she would have been home...not parading around in a bathing suit.
Even the bathing suit doesn't make sense...so she went swimming nearby and wore her wet suit to the party??
Her choice of wearing a bathing suit under her normal street garments has been explained elsewhere. Specifically, it has been pointed out that many girls in that age bracket did that so as to be able to willingly engage in "playful" behavior, but still be able to prevent (if she wanted) the boy from getting from third base to home plate.
Regards,