Does she work for the parish as a permanent staff and under its payroll? I cannot imagine a situation where I would teach something that I do not believe myself unless I am a History teacher or doing a paid job.
I suggest it would not be to the best ineterst of both parties (the parish and her) to allow the situation to continue. One may be able to give an impartial teaching but unconciously one’s unbelief may show in body language and nuance, like one’s can be cynical about the sunject. Normally these can be picked out by the students and I don’t think that is good for the objective of the RCIA. Anyway, I have yet to see a self-declared unbeliever teaches in the RCIA.
We already have the situation of non-Catholics teaching in our parochial schools, now we have non-Catholics teaching RCIA???

What in the wide world of sports could this parish priest be thinking? It is bad enough that we have poorly catechised Catholics attempting to teach RCIA, but NON_CATHOLICS??? Be like me teaching moslem “RCIA”…yeah!!! Lemme at 'em! I’ll “teach” 'em,hehehe.