Yes taking a hot shower when you have the flu is good for you.
The hot shower will wash away germs from your body and the hot shower will help with any congestion and make you feel much better.
If you're feeling strong enough to take a hot shower then do so as you will feel so much better.
When I have the flu and take a shower I feel a lot better as the germs have washed away from me and it prevents the germs from infecting me again.
Just like you should wash your hands often when you have the cold or flu you should wash your whole body with hot enough water and soap to kill germs.
The flu virus can live on your body as well but mostly it gets into your body but still taking a shower is good when you have the flu or cold virus.