The flap opens when the funnel or the gas pump nozzle is inserted. It’s spring g loaded. There is no locking mechanism because it isn’t necessary. You can’t siphon gas nor can anyone put anything in without the special funnel.
It means she left with the only working key and it’s letting you know not to drive off without a working key, Try it with her fob only. Then check your fob batteries.
Main issue is the water pump failing and taking out the engine but I think Ford revised the water pump to make it less likely. Changing coolant frequently will help. Edges with the same type of powertrain can easily go 200k-300k.
Same paint but the bumpers are typically painted elsewhere plus they are plastic vs metal which can change the appearance. Prep is different. Common issue and repainting will fix it.