This might be hard.
My suggestion would be to go to a restaurant that serves "small" plates; your friend will be able to select only one or 2 plates and share the rest with the others.
You could also try either "Aux Vivres" or Chuch (Chuchai), both are vegetarian/vegan; they might have some lower cal dishes, or might be easier to ask for them.
My mother is a avid WW member. Generally speaking, vegetarian is lower calories if you stick to non-creamy offerings. Aux Vivres is a good choice. It is gourmet but it isn't fancy though.
If you want something higher end but still weight watchers friendly go for fish. Either a sushi place (not a all you can eat) or a place with decent fish options.
Avoid italian or indian. Their menu will be difficult and tempting to a WW.