You don't have a mental intuition for your daughter, but you are probably very familiar with your ex's pattern of abuse, and you also probably understand the character traits your daughter has that are similar to your own and which make her vulnerable to his manipulation. I'm wondering how old your children are. At a certain age, minors are allowed a say in which parent they are able to live with. It might be to your advantage to check into what the laws are governing child custody in your state, if you haven't already. I ended an abusive marriage with a manipulative narcissist two years ago. Healing from that is a long process. Last summer I thought I was ready to start considering a new relationship, but I was wrong. I'm still a magnet for that same awful personality disorder. Wishing you the best.

First, I'm sorry that your daughter and you have to go through this. I can't make any guesses based on the information in your post, but this is the general outline of my hypothesis on "intuition" and psychic abilities. This may be relevant but probably isn't.

We have been taught that we are limited to five senses, but that's not correct. We sense hunger, cold, thirst, equilibrium, spatial proximity, etc. In my opinion (always be skeptical of that) our brain processes a lot more input than we can consciously process. On a subliminal level the mind creates an information triage station. It determines the most important input, for example the smell of smoke when nothing should be burning, and sends that to your conscious mind, while a lot more info is filed away subconsciously to be processed later or dismissed.

I think (opinion again) that we act on sensory input that we're not even aware of at times.

Stay calm. Think clearly. The best thing you can do is show the authorities that you are the reasonable one, the parent. What you're going through would threaten anyone's sanity. So, your composure is your best way to get custody. Meanwhile, be there. Visit your daughter whenever possible. She needs your stability; be her rock. You need support through this, so seek out a therapist if you currently don't have one. My own mother heart reaches out to you.

Very sad for you. These are the times we wish to be in the old west.

Intuition? Naw. You have something better and deeper than that: you have empathy.

When you get a chance to do so, use that empathy! Talk to her, listen to her, and don't sugar-coat your own experience or downplay hers. I wish you the best.

I think there are connections between people that are more than purely physical. I believe you did have some intuition of something going on with her.

I think it’s native intuition. You know what you went through and you can roughly guess the progress of their relationship. Undoubtedly, things could come to a head prior to a visitation.

I do not know what to say. You probably sensed that. As a mother we have some connection with our children, 6th sense as well? Not sure.
Like @donotbelieve said, keep calm and think straight. Make sure you do not get off of your tracks, you need to get stronger and be there for them.
I'm so sorry you are going thru that.