Dad talking about periods w. daughter. Is it wrong ? (Disclaimer : I’m the dad)

First of all, we’re a separated couple with a 9-year old daughter. We share custody 50/50, and although we do keep a fairly good open communication between my ex and I, we’re really not best friends and there are a couple of sensitive topics we still have difficulties talking about. An additional information I should share here is that my ex is rather conservative and uptight, whether I’m very much liberal and laidback.

This is just to give you a sense of the context.

Our daughter is very smart and sweet and obviously just as curious as any other child of her age.

Couple of months ago I went to the cinema and watched a movie called “Are you there god, it’s me Margaret”. I absolutely loved it. It was fun, very smart, yet realistic, and the topic (bodily transformation of pre-teenager girls, among other things) was - IMO - wonderfully treated.

I learned afterwards that it was the adaptation of a great book by Judy Blume.

I instantly thought that it was a great movie for my daughter to watch. Given that we recently moved to a new place, with a new school, I felt that this would be very relatable for her.

We did watch the movie at home together and she obviously had lots of questions (during and after the movie). She loved it and couldn’t wait to learn more. My opinion is that - regardless of the topic - a parent should never shy away from a question, and I always try to answer all questions, acknowledging that I don’t know and I will look the answer up if that’s the case.

Given the nature of the topic, I explained to my daughter that her mum was probably better equipped to answer some specific questions (all the intimate, practical aspect for example - does it hurt, what to do and all that).

Everything went fine (this was a week ago) up until this morning where I get a message from my ex visibly furious that I watched this movie with our daughter.

To her defence, I didn’t tell her we watched that particular movie, nor the fact that we had a conversation (very short and “high-level” really) about it after. That’s on me. I could have informed her.

Still very pissed reaction from her basically saying that she’s the done who should be handling “those topics”.

I know that this has a lot to do with “power struggle” due to our separation. She’s a very controlling person and she’ll always find ways to try to oversee how I educate our daughter.

My question is, was I wrong to watch that with my daughter and discuss it ?

[EDIT] Thanks to everyone for your kindness and comprehension. Did not expect so many responses and so much support 🙂