I have no idea of the proposed project. Have you thought of a low tech solution to electric pumps? That seems to be your first concern. Windmill pumps have been around a long time. Ram pump? Rain water harvesting? How would you design a low cost, low tech hydroponic system. Can the system be watered from an IBC tote that is filled when water is plentiful. Vandalism sucks, in our community greenhouse I placed the solar battery banks, pumps and aerators under IBC totes filled with water to prevent theft. Take a moment and see if you can come up with solutions to your objections that would let the proposal work. Point out your concerns and talk with her about them. Including her in addressing real problems you see, will give her a sense of inclusiveness. Accepting her idea but asking how to address your concerns. Pumps, water vandalism, brainstorm with other volunteers. It is so hard to maintain and expand volunteer bases a hard "no" can chase them away. Encouraging ideas, projects and problem solving with volunteers give them a connected desire to return. Would, let's say rain water collection be adventageous in other parts of the plot? Could her hydroponic system be an value added system if it collected excess water? Love the idea but what about? Initial open minded acceptance and then asking about how to address obvious problems. One needs to develop a solution based mindset when presented with new ideas that come along. It might not happen but proposed solutions might turn the light on for other projects.