You guys have done a greatjob of identifying possible issues & solutions. I am betting on the gas cap vent not being open & or over chocking.
Normally an engine will start with the gas cap unvented, but the engine will just stall unexpectedly after running a while. Sometimes the pressure will rebuild in the tank from the evaporating fuel and equalize things (if it's warm weather) and the engine will start again, and run for a while, before stalling again unexpectedly.
It can cause a silly feeling when one then discovers and opens the air vent on the gas cap and the problem is solved. I speak from experience, and experience, and experience...LOL.
Particularly, a visual clue can be seen if one is operating an outboard motor that unexpectedly stalls when under way. The clue to the unvented tank's cap will be that the gas hose's priming bulb will be collapsed because air is unable to replace the fuel burned from the tank and the soft rubber priming bulb collapses, and the engine starves for gas.
Let's hope Lee-Ann's problem is something this simple. Those little Yamaha engines typically start very easily. I can almost rely on mine starting on the first pull.