My mom came with me to meet my therapist. It was not helpful as it only gave her more ammunition to use against me, as my therapist is trans and she doesn't believe she passes. It's sad she couldn't see past her appearance because the whole session was about how we are to deal with grieving and ways that I could help my family through this. It was a pretty objective look and she mainly sympathized with my families concerns and fears. I don't know. Maybe it doesn't matter whether the therapist is a gender therapist or not. I think what's most important is that she talks to someone who can help her adjust to your transition. I don't know if she needs a gender therapist in particular for that. Since she isn't transitioning, her issues are different even though they are related to your transition. Remember, one session isn't going to change things. The only thing that will allow most families to heal is time. And remember they will go back and forth. Some days things are good with my mom. The next day, like yesterday and tonight, I am a warped disgusting embarrassment who mortifies her. Progress is rarely achieved on a continuous path. There will be bumps along the road.
Maybe you could go to a trans support group with your mom? That may help. However, keep in mind, she may use the appearances of others against you. I have learned this the hard way. In that case, there are lgbt support groups for parents as well. That might be a good step for her.