Answer:
The best place for your neighbour to put the bird bath would be at the centroid of the triangular yard. The centroid is the point where the three medians of a triangle meet, and it is also the point that is equidistant from all three sides of the triangle. This way the bird bath will be the same distance from each edge of the yard, which is what your neighbour wants. To find the centroid, your neighbour can first draw the medians of the triangle and then find their intersection point.