Sponsors who can’t make it to the social often leave word with the sponsor coordinator, and it gets passed to the plebe. Or, the sponsors will get the contact info and contact the plebe once PS is over and the plebes have email and phones. Or, sadly, it could be a ghosting situation, though that is the least likely.
Once the ac year starts, though your DD will be busy, she can stop by the sponsor office to let them know or email them. See contact info for Rose and her team here:
Sponsors have to check in at the start of the sponsor social, and their presence/absence gets marked on the master list. So, Rose and her team will know which sponsors were there, which not.
Occasionally, we have missed a sponsor social due to travel. We called the sponsor office in advance and asked them to let the plebe know. More often, we usually had an upper class “sponsor son/daughter” in the detailer group, and passed them a note to get to the plebe.
She should sit tight until she’s finished PS and settled in her ac year room. If no word, she can let the sponsor folks know.