I would reduce this to two short declarative sentences and eliminate the irrelevant stuff. File a complaint with UA and note that you are filing with DOT as well. Make sure you do file with DOT.

On the spot, you really are in a pickle. You could raise a real fuss and ask that the Captain become involved, but you run the risk of being off-loaded or worse.

It isn't going to take much for the FA to justify ordering you to move, including a simple assessment that the injury left her concerned for other passengers, but the specific circumstances here do suggest that an investigation is appropriate.

You won't get anything back other than a cut & paste, but UA does follow up and the mere fact that the FA has to respond internally will likely end her practice.