@jamesf123 For some reason, people start looking differently at you once they find out you don't do things the same way they do. Nutrition is one of the hottest topics, especially lately. What I do in this type of encounters is listen and respond calmly and in time, people either start paying attention to what I'm saying or we go separate ways. It seems your trainer is an average I-know-it-all and doesn't care much about educating herself too much, and what's problematic, she doesn't listen to you as a client and a human being. I've met my share of trainers in the past decades who are exactly the same, what I've noticed as well in the past years is that there are many "trainers" who learned everything they know through Instagram and ads.
The same happens to me all the time, once people know that I'm a vegan, they say I secretly eat meat, otherwise, my body would not look like it does, nor would my endurance be as high as it is. I learned to deal with them in an easy way, but it does take time and patience. For some reason, people get pissed of the most when you reply kindly and with a smile
There's a lot of research out there today in favour of consuming non-animal food. Most of it is hard to digest, to get people interested, articles like
https://www.plantbasednews.org/lifestyle/identical-twins-compare-vegan-meat-diets and
https://www.plantbasednews.org/lifestyle/-ironman-athlete-transforms-vegan-diet are a great conversation starter
In your case, I'd ask myself whether the trainer is worth the time and effort, her reaction could simply be because of a bad day, or she could be hard-headed. Personally, I'd give it a try and talk to her to see what her main concern is, if it doesn't help, I'd thank her for the past year and move on, finishing it with So Long, and Thanks for All the Fish