Neighbour fence dispute leaves me questioning my moral ground

Paid to put a fence in a alleyway which is in between two houses , each owner has approx half the alley each. The customers neighbour is disabled and erecting a fence will restrict her from getting her mobility scooter to the back of the house for storage and charging. We had a conversation and it’s her only independence, there has been a little disputed with my client objecting to a shared drive for her husband to park the car close to the door to aid her disability, this is after my client approved it. Seems my client is being difficult and Inconsiderate. My question is not should I do the job or not but is there any legal argument my clients neighbor has to contest and stop the build of this fence . Thanks