As a spectator event it is superb, the atmosphere is amazing and much better to be there part of it than watching on TV.
I think it's much easier for runners to see spectators...can you make a banner or a flag of some sort? A bamboo cane with a "hi Gizmo" sign on top or something similar?
Then you can decide roughly where they are to be, on which side of the road, and you can pick them out.
There are alphabetical meeting areas at the end, so you can meet up under A pre arranged letter. Or you could meet in a pub?
If she can get there, she will love it, whether she sees you on the course or meets you at the end.