Bona-fide resident status requires IRS approval. Most Ex-Pats use physical presence test ---using a test period of continuous 12 months , show that the person has been away from the USA at least 330 days( 24 hr. ) .
From what I see in your post, you should use test period of 08/26/2018 ( assuming her leaving USA on 8/24/2018 and arriving in the UK on 8/25/18 -- the first full 24 day being therefore 8/26 ) through 8/25/2019 and show her travels to the USA for any reason as required for the form 2555. This should qualify her for foreign earned income exclusion --- note that this is allocated based on the actual days present in the UK and earned from a foreign entity.
Does this make sense ?
