So, here's a new picture from that day. The girl who shared it said: "stevie's wearing her mom's wedding dress. they were paid $50 for the performance. (they were friends of friends.)" and her mother (who was there) added: "The music was background (no dancing)but definitely NOT a hippy wedding".
Edit: I've asked for a location and she is checking, believes it was in Saratoga CA.
Edit 2: The wedding was at Villa Montalvo in Saratoga, CA in August of 1971.