American Express - Membership Rewards USA

[Duffa]

Question from family member resident in the Big Apple.
She has 500,000 membership rewards on a US Platinum Amex.
All I can find is the small print that they charge $0.0006 per point to convert to air miles but can't see which FF programs they offer.
She wants to fly J from US to UK - any ideas on who best to redeem/convert to?
Delta and AA would be her choices

Thanks

Duffa

 

[Duffa]

I forgot to add she has a Barclaycard Arrival+ - I think that is only cash for travel tickets