Hi I am going to the States. If I use Revolut to change my GBP to USD and then use bank transfer on Revolut to my sisters US account (she is a US citizen) so she can get USD out for me free of charge from her own bank. Will I incur any charges or additional fees?
What you are proposing should work fine. There shouldn’t be any fees, especially as Revolut sends USD transfers to US accounts via ACH from Community Federal Savings Bank, not via SWIFT.
You will not incur any charges or aditional fees from Revolut- whether she will depends on her bank.