"We met Sahar Al-Faifi to confront her over concerns we had over antisemitic social media postings.
"Ms Al-Faifi apologised to us and made some amendments to her social media output. However, we were clear that the situation still remained unsatisfactory."
The Board clarified it had asked her to edit or delete some of her social media posts from 2012 and 2017, but that the amendments had not been made.
She changed a December 2012 Facebook post about Hamas leaders giving a victory salute to say they were greeted by "cheering crowds", which the Board said "does little to change the fact that this post is promoting 'a mighty victory' for a proscribed terrorist group".
Her 2017 post after the London Bridge attacks still linked "pro-Zionists" to the attack, which was carried out by supporters of Al-Muhajiroun and Isis and left eight dead.
The Board said this was "utterly baseless, and is clearly an antisemitic conspiracy theory".
The spokesperson added: "This was a significant time ago, and according to Ms Al-Faifi’s apology, she has learned a lot since then. We would have hoped that deleting these two posts in their entirety should not have been a question.
"However, after 18 months of waiting for her to delete them, Ms Al-Faifi’s resistance to doing so raises serious questions.
"It is also worth noting that Ms Al-Faifi remains a Regional Manager for Mend, a highly problematic organisation whose activity risks increasing hostility and suspicion between the Jewish and Muslim communities, rather than building trust and empathy."
A spokesperson for Plaid Cymru said: "We have taken immediate action to suspend the person in question. We will investigate all allegations.
"Plaid Cymru will not tolerate antisemitism, racism or intolerance in any form... It is not a part of the Wales we want to build."
