The wood trim will not handle the high moisture of the new shower. I would replace the wood trim with an attractive tile. I recommend marble for the window opening. Cut the tile deeper than the window depth and enclosure combined, so that the enclosure will fit tightly around the tile, and is slightly recessed. Be sure to use adhesive around the window opening to hold the enclosure in place, then caulk the joint between the enclosure and tile, and seal the grout.