When she discovers that she let in a strange being in the guise of her dead son, she will be forced to make a decision, before the damage is greater.

Heavy, getting a Pet Cemetery vibe from this.
Based on your second revision: "Pressed between an inquisitive priest and her memories of a mother, she must decide on the return of her dead son, before someone else does."
I’m going to take some liberties with your story but it sounds like it begins when her dead son returns, then she is corned by a priest and her shattered mind, and the decision is to re-kill (or not) her son by whatever means needed before the church intervenes?
So, make this your own, but leaning towards:
“When the manifestation of her dead son appears, an overprotective mother must learn to let go before her inquisitive priest intervenes to destroy the abomination”

Take care.

Faltaría un desencadenante.
"Presionada entre un sacerdote inquisitivo y sus recuerdos de madre, deberá tomar una decisión con respecto al retorno de su hijo muerto, antes que alguien más lo haga".

She will be forced to make a decision? I don't know what that looks like on screen.