I can relate. My daughter was in a wheelchair on our recent trip.
If she doesn’t want to do a scooter (which actually sounds like the best idea IMO), then tell the bus drivers that she can only transfer once she’s on the bus. If my daughter was in the wheelchair when they arrived, they always offerred assistance; the busses have some way of getting the wheelchair on the bus without lifting/carrying. If we were ready for them (she was already standing and the chair was folded), they never offerred.