I don't think they need to match exactly, but they should look as if they belong in the same home. Personally I don't think a formal/traditional one and a rustic one really work well together. A home should have a cohesive style.

The two fireplaces don't have to match but I would try and make sure they are similar. Maybe consider doing a white wash on the fire place that is more rustic to tie them together.

My thoughs exactly. What if she put the barn wood on the upper wall in the living room too - the one that has the white surround? It's a stanard height ceiling, where the family room is a two story wall and presently has no mantle. It might be enough to tie them together. She does not want to have a formal surround in the family room if possible. The fireplace is not bricked, it is just drywall with some 1980's marble around the opening and a door/screen. She wants to somehow cover or paint or tile (???) over the marble. Thank you again.