Fit to Fly test to visit my Spanish family from the UK

Dear all, I am wondering if anybody in similar situation. My Mother, UK citizen is trying to visit me (German citizen residing in Spain) in La Manga. What are the current Diagnostic tests requirements for people who did not have Vaccine yet? There is a conflicting information depending on which website you go, some say that Only PCR (NAAT) tests are accepted, some say that Antigen Fit to Fly test is accepted. She now has only 4 days left before departure and PCR test simply not possible, but Antigen test Fit to Fly has been ordered through Project Screen company (delivery the exet day!) Has anybody flew recently from the UK by Ryanair? Do they allow this type of test? Spanish side I think is OK, it is the UK side that is more restrictive now.

I would really appreciate any help, I have not seen my Mother since the beginning of Pandemic!