Hello, I hope you are well. My name is***** am a solicitor advocate and I will be assisting you with your question today. I am very sorry to hear of the problem you are experiencing and I will do my best to help you with this matter.
Very sorry to hear of your relative.
Unfortunately, to,visit the USA as a visitor, you need either an ESTA or the B2 visa.
In your case the B2 visa. Until you have had your interview and granted the visa, there is no way to enter the USA. Even if you had the B2 visa now, there is still a ban on entry to the USA from the U.K. visa or not.
You would need to make an application to the embassy in London for a NIE to enter the USA during the current travel restriction.
The on,y ground available would be humanitarian, but unless the relative is very close to you and would be dependant on you, the application is likely to fail. I have known of a number of such cases am they have failed.
The NIE national interest exemption, is very hard to obtain. You would need to demonstrate why granting you a NIE is in the national interest of the USA.
Sorry to say, but at the moment until your visa is granted and then travel restrictions lifted, you are stuck with online video messaging.