Having recently taken my father in a wheelchair to SFO, i can understand your concerns but i would suggest you should have taken greater steps yourself.

The first thing i did when making the booking was get on the phone and make sure my needs were noted in the booking. This included the need for seats next to the toilets. Airlines do allocate seats where a medical condition requires it.

I also pushed the wheelchair myself only surrendering it at the plane door, thus keeping me in control.

I have to say the wheelchair helper i had at LHR on my return was absolutely brilliant.