I am planning a trip from Washington/Dulles to Windhoek, Namibia via Frankfurt. The FRA to WDH flight will be on Discover Airlines (formally Eurowings and affiliated with Lufthansa). I am US-based, a Mileage Plus member and do 80% of my flying with United. When I log into my United account to look at options and make this reservation, I cannot get beyond FRA and instead I get options to fly via South Africa (UA & Airlink) or via Addis (ET). Knowing this background, I'm thinking my options are the following, but would welcome insight from those of you more knowledgeable...
Option 1: Make a return United booking between IAD and FRA and a separate booking with Lufthansa/Discover Airlines for the return trip between FRA and WDH
Option 2: Make my entire flight reservations with Lufthansa. This would be easier and more efficient, but I will lose any United miles I would get (at least that's how I understand it).
In advance, thanks for your time, advice and/or other options for this route.