First, welcome. Lucky to have your wife involved in the shop! My first thought was it's an added piece and that would still work if you matched the grain carefully and used the same wood species.
You will need a number of bits to carry this off. The panel groove can be cut easily on all four sides with a slot cutter. Then use the wide panel bit to cut just the horizontal pieces (rails) and trim the curved section to fit against the stiles (vertical) If you do this in one piece, you will cut the rails wider than the stiles to account for the trim section, which will be the width of the bit.
You will also be using roundover bits in 1/4 and 1/8th sizes to soften those hard edges.
So you are talking about at least 3 bits. It is very easy to get stuck on the idea of using a single bit, which probably doesn't exist. The good news is this isn't a particularly complex panel door to make.
Personally, I'd make it in two pieces, being extremely careful to fit the trim piece as precisely as possible into the door. I'd take plenty of time finding matching grain and color so they finish the same. You can use your router and bit to shape the trim piece separately. Cut the trim piece 1/8th inch wider that two times the bit's radius. If the bit cutter radius is 1.25 inches, rip the cut 2 5/8ths wide, then run it through twice, once on each edge, then rip it in half and you have both pieces.
Getting all rails and stiles the exact same thickness is really important or you have to do a lot of sanding later. Cut with the face down on a table, face up when cutting freehand. Forget about cutting the trim piece freehand.
Finally, the best technique I've ever seen is in videos by Marc Sommerfeld, which you can find free on YouTube. He sells routing gear, but he was a master cabinet maker and his technique is uncomplicated and very precise. I have several of his matched bit sets and bought all of his videos on dvds. I watch an appropriate video whenever I do a project because they are so helpful. When you don't do a lot of the same projects, you forget details and spoil expensive wood. YouTube, Marc Sommerfeld will be very helpful.
I make a lot of picture frames, which are devilishly precise on cuts. One thing I discovered is that sanding finer than 220 grit was counterproductive. For exquisite finish, I prefer to use scrapers, which are cheap but take a little care to sharpen and use properly.
The more I do, the less I accomplish.
Last edited by DesertRatTom; 07-12-2020 at 09:55 AM.