Personally I don't think you need to worry at her shooting ?-flares at you. People tend to avoid subjects they're uncomfortable talking about, and from what I read she's not exactly feeling snuggly toward your transstatus. Thus, chances are she'll do anything in her 'power' to avoid talking about it - your 'frightening' stories might cause her to check under her bed and her closets before sleeping..
So, in my opinion best you can do is land a good first impression by being yourself and probably pick up some of the things Cynth lay out in her post. If mum does launch a canonball just keep your answers short and simple; "So.. You're a guy?", "Yes. I'm really glad to finally meet you, I care a whole lot for your son." Just my paired cents.