I came out to my mom about being pansexual about 6 or so months ago. Last month when I talked to her about the person I've been dating for years being transgender, I was expecting questions like "Isn't this really sudden?" or "Are you sure he's not gay?" but no, my mom asked "I thought you were straight. Do you even like girls?" I wanted to scream. I had three panic attacks trying to figure out how to come out, and she forgot about it. She still won't refer to my girlfriend as a girl, or my girlfriend, or by the pronouns she wants, no matter what I say. It honestly feels like she forgot again.
A lot of parents conveniently "forget" because they don't want to deal with it. In other words, denial. Just keep bringing it up to her. Maybe have her meet your girlfriend as well.
I came out every few months for 11 years as bisexual, and my parents didn't actually believe me until I began dating someone of the same biological sex. It takes time.
She's known my girlfriend since day 1. She's all for "LGBT Rights" until someone brings up the T. A transgender woman who lived down the street from me was arrested on false charges and all my mom said was "Who would let their kid be a disgusting crossdresser like that?" Now that she knows my boyfriend is my girlfriend, she doesn't bring up anything anymore.
I'm very sorry to hear that (*hug*). My honest advice to you would be to just keep coming out until she finally gets her head through it and accepts it.
