What linkat said.
Also, sounds as though her actions are coming from love and concern. Some people are very frightened right now and I’m thinking your daughter may be expressing her fear as anger.
I would assume she is more concerned about her boyfriend visiting you than her brother because she loves him and is also fearful he will infect her.
Not sure why he is visiting you? Are you close or is he concerned for you?
Secrecy is not going to help