If the couple are family that you saw at least during the holidays most years; the 25th is a noteworthy anniversary ... it would be a nice gesture to send a gift.

However, sending money to the daughter could further complicate things if the trip doesn't come off.
Instead, you might advise the daughter that you are going to send flowers to their room at the B&B with a note expressing your *personal* well-wishes ... and for her to let you know the name of the B&B and the date of their stay. If she insists that she would like you to contribute to the B&B instead, tell her it sounds like a nice idea but you prefer to send a personal gift, and in fact intend to do so whether they go to the B&B or not.

After confirming the reservation just prior to their arrival, have FTD (etc) deliver flowers to their room with a nice note. (or flowers and a bottle of champaign etc.)

If the B&B trip does not come off, send the flowers and the note to them at home anyway ... it's a classy thing to do.

The daughter shouldn't fault you ... you did honor her parents with a gift. And the gift is the choice of the giver.

She's young and used poor judgement. Maybe her intentions where upstanding, however she should have called people on the phone indicating she wanted to do something for her parents, and that "if we don't get a party together for them" would people be willing to put in on an alternative gift ... like a stay at a B&B.