I strongly recommend you don't let your dc go.
Giving dc sweets and glitter is incredibly manipulative and the counsellor should not engage these young children in this way. It reinforces the power imbalance between the counsellor and child / client and leaves the child feeling indebted / grateful for the sweet and glitter as well as the special attention this person is giving them.
Almost all of these 'counsellors' have done a fairly short training and they are NOT accredited counsellors they are child mental health practitioners. You could teach yourself the techniques they use form a couple of book son the topic on Amazon.
With or without the worry about trans ideology it is a highly questionable intervention, I know because my dc was offered it because her friends in school treated her badly and she was shy. One of her friends has been with our school's mental health practitioner for 3 years I didn't want this for my dc.
Instead, I bought a worry journal off amazon as well as a gratitude journal for her and for myself and every so often we sat together and filled in our journals and shared and talked about what we had written after. This helped normalise that everyone can feel bad about things or themselves and their relationships at times, even parents and that if we try and reframe some thing in a more optimistic and positive way we can see other aspects and opportunities to overcome difficulties, that are part of everyone's life. This helped her not fear feeling sad or anxious but accept it as part of a wide range of human emotions. We also talked about practical steps to tackle things that are causing issues at school. For us this approach worked well. I do not support half-baked pseudo psychology from strangers who for the most part have had max 12-18 months of training, many haven't been to university. There are some excellent child CBT books you can work through as well although it helps if you have done cbt yourself, which i have.
I studied psychology at university and have read dozens of self help and life philosophy books over the years. I am also a trained peer supporter for a charity. I believe firmly that empowering children so they feel they have some control and helping them see they can change many things that are difficult or not ideal but some things cannot be changed and they have to put up and adapt. That's life and it's best they learn this without being treated with special glitter and given treats to make them feel like they need to be mollycoddled. To me this approach reinforces the idea they are damaged and helpless rather than building them up. Most issues are part of normal life for kids, and if they are not, it's usually bullying related in which case the school has to deal with the bullies not give glitter and sugar to kids who are being bullied or there is neuro diversity in which case they will need specialist support, not a half baked mental health assistant. Children are vulnerable by definition and easy to influence, I do not at all trust anyone who will keep information from parents. It's a safeguarding red flag. In our case, my dc was actually given one of these session without the mental health support assistant actually obtaining my consent 😂Safe to say, this was the only session that I allowed to happen.
You should also know that your dc will miss out lesson time for this highly questionable intervention. Don't do it is my advice. Most issues can be resolved with loving and educated parental support.