if he dropped her off at 2:30 and then returned an hour and a half later pretty f'd up, then there is a good probability that he HAD been drinking when he had her and when he drove with her in the car. i think IT IS a big deal.
how simply terrible for your girl. yes that's my father over in the corner, mumbling to himself and drooling.
i agree that non-invitations are to be considered. also NOT relying on HIM for anything......not.one.thing. no cake, candles, matches, nothing. your daughter is old enough to have discussions with her on why this is.
it might be time to re-address the parenting plan.