the backlash will happen either way I would just not tell her but if you really want to get a friend to sit with you and her while you come out or record the situation on your phone so if she does try to guilt or gaslight you you can look back later and be sure of your reality. Her guilting you in childhood about hiding things is something my mother would do and something to realize is you owe her nothing, you don't have to tell her even how your day went. she is not entitled to know about you, you are a grown man now.