The lake was part of the retirement community's property therefore they are responsible to keep it safe for their residents. All they had to do was put up a wire fence keeping gators out of the water, have a monitor there like a lifeguard to police the areas and watch for dangers, put up warning signs along the water, or at least monitor it for gators and this one had been there so long, it had been named by some of the people.
You could see the gator coming in; a monitor there could have spotted it and warned her. Still, just better to put up a short anti-gator fence around the water's edge.
The owners and family will probably reach an equitable out of court settlement for culpable negligence.