The production company behind her TV adaptations had informed her they would no longer be able to pay her royalties through British banking, and that if it knew she intended to donate to PA the company would be liable to prosecution . Her publisher Faber has also come to the same conclusion.

There's a characteristically interesting look at this by David Allen Green, including:

one would think it unlikely that the British state would prosecute a famous Irish author and an even more famous publishing house. But little about the terrorism law of the UK makes sense at the moment, since the ludicrous decision of then home secretary Yvette Cooper and the Home Office to proscribe what is essentially a direct-action protest group as a terrorist organisation.

His view is that they must think there's a reasonable chance of it coming to pass or they wouldn't be taking the financial hit.

Of course, it's great publicity for them and her, so maybe it balances out in the end.