Although I've been on HRT for a few years and got SRS surgery in August last year, I only fully came out to my 80 year old mother this past christmas (although she's been calling me her daughter for a long time because although I like being andro, I'm definitely on the female side of things)... I not only came out about being trans and getting the surgery, I also came out (along with my lovely wife) to being in a long-term poly relationship with a girl my mother has met but never realized what she was to us... lol! That was a fun conversation, aided by a box of wine. But she took it kinda like this: lots of questions, but thankfully, with less blaming other factors and more just trying to understand. The first point was a big one: personal safety. Undoubtedly trans people are at a far higher risk of personal harm than even just LGB people... but I also reminded her that a lot of those stats are a bit skewed by the sadly large amount of trans women working as escorts due to necessity (true stat, look it up), plus I don't really hang out in nightspots after midnight anymore, so that limits my risk. I also reminded her the suicide rate of untreated transpeople is also very high, so... also, why would I put myself into such danger without feeling it being the only only thing that would help me? She understood those points well, I thought, so maybe you can try them on your momma. Good luck.... but it sounds promising so far.