INHERITANCE OF US IRA investments

[Lawrence210794]

My wife is the beneficiary of a share of two separate IRA accounts with her cousins from her late uncle who died in massachusets earlier this year.
Apparently she seems to have to pay 30% tax at source? Is this correct? As she is a UK non tax payer. Other UK beneficiaries are tax payers.
Her uncle was American with no UK connection.
Your help would be appreciated as the forms are horrible.
taimar