She's afraid and concerned. Explaining to someone who doesn't understand what it feels like and what will happen will sometimes not get past that mental road block. When people receive news they find shocking and upsetting they need to progress emotionally through a few different stages before they get to the point of acceptance... sometimes that can take a lot longer than we would like. Some of those stages are: denial > anger > bargaining (attempting to control the situation) > depression > acceptance. (Some models have additional steps along the way.)
Sounds like your mom is at the denial stage, so be prepared for a very bumpy ride before you get to the end of her process. Your journey is also her journey - she may not reach acceptance until you've fully transitioned and are living successfully as a man. Hopefully it will be sooner than that. She may not be showing much love, respect and understanding towards you but that's what you'll need for her if you're both going to get there in the end.
All the best, hon. Stay strong. Hugs.
