We stayed at the Amrath Hotel (or Grand Hotel Amrath, not sure how it's listed). We booked through Hotels.com. Your friend should have free wifi and should be able to book online. The hotel was very nice and is easy walking distance from Central Station. We took a taxi from the port to the hotel. I think it was about about 30 euros. If she has travel insurance, that will pick up the difference between what Royal pays and the cost of the hotel.
Before she leaves the ship, Royal will give her a paper that will tell her who to email from Royal about getting the Certificate of Recovery. Mine was jw_frontdeskmanager@RCCL.com. When I emailed him on Day 8 after I tested positive, he gave me the information on MobiDoc. The address is covid.mobidoctor.eu. It is an online consultation with a doctor who will then send her the CofR. Make sure to tell your friend that she will need to log into that website to get the CofR. I thought it was coming through my email but it didn't. When I finally found it, the doctor had sent it immediately after we spoke. So if your friend needs it to fly home, she'll have it right away. Setting up the consultation sounds a little involved but it really isn't. I'm not tech savvy at all and was able to do it.
Another tip - we did not have an adapter when we got to the hotel. Ask and they will give you one with a deposit.
I agree with your friend. The communication from Royal was not good. Seemed like one person didn't know what the other was doing. I wish her luck.
Your friend can email me if I can be of help. kandbe24@ptd.net