Is twice weekly therapy against ethical guidelines?

Essentially what the title says, I've had 2 therapists say it word for word. "It's against ethical guidelines of psychotherapy"
My former has been unwilling to budge on that stance as it's "her obligation to prevent potential harm" But I'd argue the insistent refusal to even entertain twice weekly temporarily is causing me distress and distrust. I've explained my situation and frustrations in every way possible.

So, I am wondering. Is it against ethical guidelines? My research suggests it's not as black and white as she says it is.