The day has more moving parts than the ceremony
A wedding day is a chain of pickups that all have to land on time. The bride and groom, the wedding party, family, and guests who are staying at a hotel and need to reach the ceremony. Then the move from ceremony to reception, and the photo locations in between.
The same service reaches either side of the wedding day too: the rehearsal dinner, the bridal shower, and the honeymoon departure when you leave for the airport or your first night away. Tell Shelly the whole schedule at once and she plans the vehicles and the timing around it, not one ride at a time.
Shelly's own vehicle seats up to 8. When the wedding is bigger than that, she arranges additional vehicles so the party and guests are covered without anyone left at a hotel lobby.