The list of things you need to do and have before you can allow a member of the public across the threshold is almost infinite.
We had a patient sue us when she tripped up over a slightly raised slab on the footpath ( next doors tree root) I’d only noticed it a couple of days before and had been parking over it but couldn’t fit in the space the day they took a tumble. The best of it was that she was looking at her phone when she tripped. When it was surveyed by the insurance company it was 1mm above the limit. Lesson learned and after we had it repaired we parked over the area of the carpark that was slabbed. The path was unnecessary.
I think the portaloo is a massive problem area. It will need lighting and there is the issue of accessibility for the disabled. She would need to make it clear that the premises is not accessible.
And yes the decking surface will need addressing as will the flooring in the gym. If it’s not commercial flooring with non slip capabilities it’s a major slip hazard in a sweaty gym.
Fire regulations, with electrical equipment she will need smoke detectors, fire extinguishers, a fire evacuation plan and possibly an alarm since there is a highly flammable building next to the shed. Some sort of intercom or reliable phone line for emergencies.
When you invite the general public into your premises it gets very expensive and is a nightmare in admin. Policies for everything. All equipment needs regular maintenance and inspection to meet the terms of insurance and HSE.
Fire extinguishers alone need checking annually and refilled where necessary. You need CPR training - certified - no online jiggers pockery. Basic first aid certificate. And some must be insight at all times, no swanning off on day dates or dog walks, leaving clients to DIY.
What you can’t do is just give the place a lick of paint and throw a tarp on the roof. Has she checked if the tarp is fire retardant to the specified regs? Yawn is clueless when it comes to setting up a business. As a business coach she should know all of this but maybe she never reads what she copies and pastes.